JavaScript Notes for Professionals (GoalKicker.com Stack Overflow Documentation) (Z-Library)

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JavaScript Notes for ProfessionalsJavaScript® Notes for Professionals GoalKicker.com Free Programming Books Disclaimer This is an unocial free book created for educational purposes and is not aliated with ocial JavaScript® group(s) or company(s). All trademarks and registered trademarks are the property of their respective owners 400+ pages of professional hints and tricks

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Contents About 1 ................................................................................................................................................................................... Chapter 1: Getting started with JavaScript 2 ..................................................................................................... Section 1.1: Using console.log() 2 ..................................................................................................................................... Section 1.2: Using the DOM API 4 .................................................................................................................................... Section 1.3: Using window.alert() 5 .................................................................................................................................. Section 1.4: Using window.prompt() 6 ............................................................................................................................. Section 1.5: Using window.confirm() 7 ............................................................................................................................ Section 1.6: Using the DOM API (with graphical text: Canvas, SVG, or image file) 8 ................................................. Chapter 2: JavaScript Variables 10 ......................................................................................................................... Section 2.1: Defining a Variable 10 ................................................................................................................................. Section 2.2: Using a Variable 10 ..................................................................................................................................... Section 2.3: Types of Variables 10 .................................................................................................................................. Section 2.4: Arrays and Objects 11 ................................................................................................................................ Chapter 3: Built-in Constants 12 ................................................................................................................................ Section 3.1: null 12 ............................................................................................................................................................. Section 3.2: Testing for NaN using isNaN() 12 .............................................................................................................. Section 3.3: NaN 13 .......................................................................................................................................................... Section 3.4: undefined and null 14 .................................................................................................................................. Section 3.5: Infinity and -Infinity 15 ................................................................................................................................. Section 3.6: Number constants 15 .................................................................................................................................. Section 3.7: Operations that return NaN 16 ................................................................................................................... Section 3.8: Math library functions that return NaN 16 ................................................................................................ Chapter 4: Comments 17 .............................................................................................................................................. Section 4.1: Using Comments 17 ..................................................................................................................................... Section 4.2: Using HTML comments in JavaScript (Bad practice) 17 ........................................................................ Chapter 5: Console 19 ..................................................................................................................................................... Section 5.1: Measuring time - console.time() 22 ............................................................................................................ Section 5.2: Formatting console output 23 .................................................................................................................... Section 5.3: Printing to a browser's debugging console 24 ......................................................................................... Section 5.4: Including a stack trace when logging - console.trace() 26 ..................................................................... Section 5.5: Tabulating values - console.table() 26 ...................................................................................................... Section 5.6: Counting - console.count() 28 .................................................................................................................... Section 5.7: Clearing the console - console.clear() 30 .................................................................................................. Section 5.8: Displaying objects and XML interactively - console.dir(), console.dirxml() 30 ...................................... Section 5.9: Debugging with assertions - console.assert() 32 ..................................................................................... Chapter 6: Datatypes in JavaScript 33 ................................................................................................................. Section 6.1: typeof 33 ....................................................................................................................................................... Section 6.2: Finding an object's class 34 ........................................................................................................................ Section 6.3: Getting object type by constructor name 34 ............................................................................................ Chapter 7: Strings 37 ....................................................................................................................................................... Section 7.1: Basic Info and String Concatenation 37 ..................................................................................................... Section 7.2: Reverse String 38 ......................................................................................................................................... Section 7.3: Comparing Strings Lexicographically 39 ................................................................................................... Section 7.4: Access character at index in string 40 ....................................................................................................... Section 7.5: Escaping quotes 40 ...................................................................................................................................... Section 7.6: Word Counter 41 ..........................................................................................................................................

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Section 7.7: Trim whitespace 41 ...................................................................................................................................... Section 7.8: Splitting a string into an array 41 .............................................................................................................. Section 7.9: Strings are unicode 42 ................................................................................................................................. Section 7.10: Detecting a string 42 .................................................................................................................................. Section 7.11: Substrings with slice 43 ............................................................................................................................... Section 7.12: Character code 43 ...................................................................................................................................... Section 7.13: String Representations of Numbers 43 .................................................................................................... Section 7.14: String Find and Replace Functions 44 ...................................................................................................... Section 7.15: Find the index of a substring inside a string 45 ....................................................................................... Section 7.16: String to Upper Case 45 ............................................................................................................................. Section 7.17: String to Lower Case 46 ............................................................................................................................. Section 7.18: Repeat a String 46 ...................................................................................................................................... Chapter 8: Date 47 ........................................................................................................................................................... Section 8.1: Create a new Date object 47 ....................................................................................................................... Section 8.2: Convert to a string format 49 .................................................................................................................... Section 8.3: Creating a Date from UTC 50 ..................................................................................................................... Section 8.4: Formatting a JavaScript date 53 ............................................................................................................... Section 8.5: Get the number of milliseconds elapsed since 1 January 1970 00:00:00 UTC 55 ................................. Section 8.6: Get the current time and date 55 ............................................................................................................... Section 8.7: Increment a Date Object 56 ....................................................................................................................... Section 8.8: Convert to JSON 57 ..................................................................................................................................... Chapter 9: Date Comparison 58 ................................................................................................................................ Section 9.1: Comparing Date values 58 .......................................................................................................................... Section 9.2: Date Dierence Calculation 59 .................................................................................................................. Chapter 10: Comparison Operations 60 ................................................................................................................ Section 10.1: Abstract equality / inequality and type conversion 60 ........................................................................... Section 10.2: NaN Property of the Global Object 61 ..................................................................................................... Section 10.3: Short-circuiting in boolean operators 63 ................................................................................................. Section 10.4: Null and Undefined 65 ............................................................................................................................... Section 10.5: Abstract Equality (==) 65 ........................................................................................................................... Section 10.6: Logic Operators with Booleans 66 ........................................................................................................... Section 10.7: Automatic Type Conversions 67 ............................................................................................................... Section 10.8: Logic Operators with Non-boolean values (boolean coercion) 67 ....................................................... Section 10.9: Empty Array 68 ........................................................................................................................................... Section 10.10: Equality comparison operations 68 ........................................................................................................ Section 10.11: Relational operators (<, <=, >, >=) 70 ........................................................................................................ Section 10.12: Inequality 71 .............................................................................................................................................. Section 10.13: List of Comparison Operators 72 ............................................................................................................ Section 10.14: Grouping multiple logic statements 72 ................................................................................................... Section 10.15: Bit fields to optimise comparison of multi state data 72 ...................................................................... Chapter 11: Conditions 74 .............................................................................................................................................. Section 11.1: Ternary operators 74 .................................................................................................................................. Section 11.2: Switch statement 75 .................................................................................................................................... Section 11.3: If / Else If / Else Control 77 ......................................................................................................................... Section 11.4: Strategy 78 ................................................................................................................................................... Section 11.5: Using || and && short circuiting 79 ............................................................................................................. Chapter 12: Arrays 80 ...................................................................................................................................................... Section 12.1: Converting Array-like Objects to Arrays 80 ............................................................................................. Section 12.2: Reducing values 82 .................................................................................................................................... Section 12.3: Mapping values 84 .....................................................................................................................................

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Section 12.4: Filtering Object Arrays 84 .......................................................................................................................... Section 12.5: Sorting Arrays 86 ........................................................................................................................................ Section 12.6: Iteration 88 .................................................................................................................................................. Section 12.7: Destructuring an array 92 ......................................................................................................................... Section 12.8: Removing duplicate elements 93 ............................................................................................................. Section 12.9: Array comparison 93 ................................................................................................................................. Section 12.10: Reversing arrays 94 .................................................................................................................................. Section 12.11: Shallow cloning an array 95 ..................................................................................................................... Section 12.12: Concatenating Arrays 95 ......................................................................................................................... Section 12.13: Merge two array as key value pair 97 .................................................................................................... Section 12.14: Array spread / rest 97 .............................................................................................................................. Section 12.15: Filtering values 98 ..................................................................................................................................... Section 12.16: Searching an Array 99 .............................................................................................................................. Section 12.17: Convert a String to an Array 100 ............................................................................................................ Section 12.18: Removing items from an array 100 ........................................................................................................ Section 12.19: Removing all elements 101 ...................................................................................................................... Section 12.20: Finding the minimum or maximum element 102 .................................................................................. Section 12.21: Standard array initialization 103 ............................................................................................................. Section 12.22: Joining array elements in a string 104 .................................................................................................. Section 12.23: Removing/Adding elements using splice() 105 .................................................................................... Section 12.24: The entries() method 105 ........................................................................................................................ Section 12.25: Remove value from array 105 ................................................................................................................ Section 12.26: Flattening Arrays 106 .............................................................................................................................. Section 12.27: Append / Prepend items to Array 107 ................................................................................................... Section 12.28: Object keys and values to array 107 ..................................................................................................... Section 12.29: Logical connective of values 108 ........................................................................................................... Section 12.30: Checking if an object is an Array 108 .................................................................................................... Section 12.31: Insert an item into an array at a specific index 109 .............................................................................. Section 12.32: Sorting multidimensional array 109 ....................................................................................................... Section 12.33: Test all array items for equality 110 ...................................................................................................... Section 12.34: Copy part of an Array 110 ...................................................................................................................... Chapter 13: Objects 112 .................................................................................................................................................. Section 13.1: Shallow cloning 112 ..................................................................................................................................... Section 13.2: Object.freeze 112 ........................................................................................................................................ Section 13.3: Object cloning 113 ...................................................................................................................................... Section 13.4: Object properties iteration 114 ................................................................................................................. Section 13.5: Object.assign 115 ........................................................................................................................................ Section 13.6: Object rest/spread (...) 116 ........................................................................................................................ Section 13.7: Object.defineProperty 116 ......................................................................................................................... Section 13.8: Accesor properties (get and set) 117 ....................................................................................................... Section 13.9: Dynamic / variable property names 117 ................................................................................................ Section 13.10: Arrays are Objects 118 ............................................................................................................................. Section 13.11: Object.seal 119 ........................................................................................................................................... Section 13.12: Convert object's values to array 120 ...................................................................................................... Section 13.13: Retrieving properties from an object 120 ............................................................................................... Section 13.14: Read-Only property 123 ........................................................................................................................... Section 13.15: Non enumerable property 123 ................................................................................................................ Section 13.16: Lock property description 123 ................................................................................................................. Section 13.17: Object.getOwnPropertyDescriptor 124 ................................................................................................... Section 13.18: Descriptors and Named Properties 124 ................................................................................................. Section 13.19: Object.keys 126 .........................................................................................................................................

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Section 13.20: Properties with special characters or reserved words 126 .................................................................. Section 13.21: Creating an Iterable object 127 ............................................................................................................... Section 13.22: Iterating over Object entries - Object.entries() 127 .............................................................................. Section 13.23: Object.values() 128 ................................................................................................................................... Chapter 14: Arithmetic (Math) 129 ........................................................................................................................... Section 14.1: Constants 129 .............................................................................................................................................. Section 14.2: Remainder / Modulus (%) 129 .................................................................................................................. Section 14.3: Rounding 130 .............................................................................................................................................. Section 14.4: Trigonometry 132 ....................................................................................................................................... Section 14.5: Bitwise operators 133 ................................................................................................................................ Section 14.6: Incrementing (++) 135 ................................................................................................................................ Section 14.7: Exponentiation (Math.pow() or **) 135 ..................................................................................................... Section 14.8: Random Integers and Floats 136 ............................................................................................................. Section 14.9: Addition (+) 137 .......................................................................................................................................... Section 14.10: Little / Big endian for typed arrays when using bitwise operators 137 .............................................. Section 14.11: Get Random Between Two Numbers 138 ............................................................................................... Section 14.12: Simulating events with dierent probabilities 139 ................................................................................. Section 14.13: Subtraction (-) 140 .................................................................................................................................... Section 14.14: Multiplication (*) 140 ................................................................................................................................. Section 14.15: Getting maximum and minimum 140 ..................................................................................................... Section 14.16: Restrict Number to Min/Max Range 141 ................................................................................................ Section 14.17: Ceiling and Floor 141 ................................................................................................................................ Section 14.18: Getting roots of a number 142 ................................................................................................................ Section 14.19: Random with gaussian distribution 142 ................................................................................................. Section 14.20: Math.atan2 to find direction 143 ............................................................................................................ Section 14.21: Sin & Cos to create a vector given direction & distance 143 ............................................................... Section 14.22: Math.hypot 144 ......................................................................................................................................... Section 14.23: Periodic functions using Math.sin 145 .................................................................................................... Section 14.24: Division (/) 146 ......................................................................................................................................... Section 14.25: Decrementing (--) 146 ............................................................................................................................. Chapter 15: Bitwise operators 148 ............................................................................................................................ Section 15.1: Bitwise operators 148 ................................................................................................................................. Section 15.2: Shift Operators 150 .................................................................................................................................... Chapter 16: Constructor functions 151 ................................................................................................................... Section 16.1: Declaring a constructor function 151 ........................................................................................................ Chapter 17: Declarations and Assignments 152 ................................................................................................ Section 17.1: Modifying constants 152 ............................................................................................................................ Section 17.2: Declaring and initializing constants 152 .................................................................................................. Section 17.3: Declaration 152 ........................................................................................................................................... Section 17.4: Undefined 153 ............................................................................................................................................. Section 17.5: Data Types 153 ........................................................................................................................................... Section 17.6: Mathematic operations and assignment 153 .......................................................................................... Section 17.7: Assignment 155 ........................................................................................................................................... Chapter 18: Loops 156 ..................................................................................................................................................... Section 18.1: Standard "for" loops 156 ............................................................................................................................ Section 18.2: "for ... of" loop 157 ...................................................................................................................................... Section 18.3: "for ... in" loop 159 ....................................................................................................................................... Section 18.4: "while" Loops 159 ....................................................................................................................................... Section 18.5: "continue" a loop 160 ................................................................................................................................. Section 18.6: Break specific nested loops 161 ...............................................................................................................

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Section 18.7: "do ... while" loop 161 .................................................................................................................................. Section 18.8: Break and continue labels 161 ................................................................................................................. Chapter 19: Functions 163 ............................................................................................................................................. Section 19.1: Function Scoping 163 .................................................................................................................................. Section 19.2: Currying 164 ................................................................................................................................................ Section 19.3: Immediately Invoked Function Expressions 165 ..................................................................................... Section 19.4: Named Functions 166 ................................................................................................................................ Section 19.5: Binding `this` and arguments 169 ............................................................................................................. Section 19.6: Functions with an Unknown Number of Arguments (variadic functions) 171 ..................................... Section 19.7: Anonymous Function 172 .......................................................................................................................... Section 19.8: Default parameters 174 ............................................................................................................................ Section 19.9: Call and apply 176 ...................................................................................................................................... Section 19.10: Partial Application 177 .............................................................................................................................. Section 19.11: Passing arguments by reference or value 178 ....................................................................................... Section 19.12: Function Arguments, "arguments" object, rest and spread parameters 179 .................................... Section 19.13: Function Composition 179 ........................................................................................................................ Section 19.14: Get the name of a function object 180 ................................................................................................... Section 19.15: Recursive Function 180 ............................................................................................................................. Section 19.16: Using the Return Statement 181 ............................................................................................................. Section 19.17: Functions as a variable 182 ..................................................................................................................... Chapter 20: Functional JavaScript 185 .................................................................................................................. Section 20.1: Higher-Order Functions 185 ...................................................................................................................... Section 20.2: Identity Monad 185 ................................................................................................................................... Section 20.3: Pure Functions 187 .................................................................................................................................... Section 20.4: Accepting Functions as Arguments 188 ................................................................................................. Chapter 21: Prototypes, objects 190 ........................................................................................................................ Section 21.1: Creation and initialising Prototype 190 ..................................................................................................... Chapter 22: Classes 192 ................................................................................................................................................. Section 22.1: Class Constructor 192 ................................................................................................................................ Section 22.2: Class Inheritance 192 ................................................................................................................................ Section 22.3: Static Methods 193 .................................................................................................................................... Section 22.4: Getters and Setters 193 ............................................................................................................................ Section 22.5: Private Members 194 ................................................................................................................................ Section 22.6: Methods 195 ............................................................................................................................................... Section 22.7: Dynamic Method Names 195 ................................................................................................................... Section 22.8: Managing Private Data with Classes 196 ............................................................................................... Section 22.9: Class Name binding 198 ........................................................................................................................... Chapter 23: Namespacing 199 .................................................................................................................................... Section 23.1: Namespace by direct assignment 199 .................................................................................................... Section 23.2: Nested Namespaces 199 .......................................................................................................................... Chapter 24: Context (this) 200 .................................................................................................................................... Section 24.1: this with simple objects 200 ....................................................................................................................... Section 24.2: Saving this for use in nested functions / objects 200 ............................................................................ Section 24.3: Binding function context 201 .................................................................................................................... Section 24.4: this in constructor functions 202 .............................................................................................................. Chapter 25: Setters and Getters 203 ...................................................................................................................... Section 25.1: Defining a Setter/Getter Using Object.defineProperty 203 ................................................................... Section 25.2: Defining an Setter/Getter in a Newly Created Object 203 ................................................................... Section 25.3: Defining getters and setters in ES6 class 203 .........................................................................................

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Chapter 26: Events 205 ................................................................................................................................................... Section 26.1: Page, DOM and Browser loading 205 ...................................................................................................... Chapter 27: Inheritance 206 ......................................................................................................................................... Section 27.1: Standard function prototype 206 ............................................................................................................. Section 27.2: Dierence between Object.key and Object.prototype.key 206 ............................................................ Section 27.3: Prototypal inheritance 206 ....................................................................................................................... Section 27.4: Pseudo-classical inheritance 207 ............................................................................................................. Section 27.5: Setting an Object's prototype 208 ........................................................................................................... Chapter 28: Method Chaining 210 ............................................................................................................................. Section 28.1: Chainable object design and chaining 210 .............................................................................................. Section 28.2: Method Chaining 212 ................................................................................................................................ Chapter 29: Callbacks 213 ............................................................................................................................................. Section 29.1: Simple Callback Usage Examples 213 ..................................................................................................... Section 29.2: Continuation (synchronous and asynchronous) 214 ............................................................................ Section 29.3: What is a callback? 215 ............................................................................................................................ Section 29.4: Callbacks and `this` 216 ............................................................................................................................ Section 29.5: Callback using Arrow function 217 .......................................................................................................... Section 29.6: Error handling and control-flow branching 218 ..................................................................................... Chapter 30: Intervals and Timeouts 219 ............................................................................................................... Section 30.1: Recursive setTimeout 219 ......................................................................................................................... Section 30.2: Intervals 219 ............................................................................................................................................... Section 30.3: Intervals 219 ............................................................................................................................................... Section 30.4: Removing intervals 220 ............................................................................................................................ Section 30.5: Removing timeouts 220 ............................................................................................................................ Section 30.6: setTimeout, order of operations, clearTimeout 220 .............................................................................. Chapter 31: Regular expressions 222 ....................................................................................................................... Section 31.1: Creating a RegExp Object 222 ................................................................................................................... Section 31.2: RegExp Flags 222 ....................................................................................................................................... Section 31.3: Check if string contains pattern using .test() 223 .................................................................................... Section 31.4: Matching With .exec() 223 ......................................................................................................................... Section 31.5: Using RegExp With Strings 223 ................................................................................................................. Section 31.6: RegExp Groups 224 .................................................................................................................................... Section 31.7: Replacing string match with a callback function 225 ............................................................................. Section 31.8: Using Regex.exec() with parentheses regex to extract matches of a string 226 ................................ Chapter 32: Cookies 228 ................................................................................................................................................. Section 32.1: Test if cookies are enabled 228 ................................................................................................................ Section 32.2: Adding and Setting Cookies 228 .............................................................................................................. Section 32.3: Reading cookies 228 ................................................................................................................................. Section 32.4: Removing cookies 228 .............................................................................................................................. Chapter 33: Web Storage 229 ..................................................................................................................................... Section 33.1: Using localStorage 229 .............................................................................................................................. Section 33.2: Simpler way of handling Storage 229 ..................................................................................................... Section 33.3: Storage events 230 .................................................................................................................................... Section 33.4: sessionStorage 231 .................................................................................................................................... Section 33.5: localStorage length 232 ............................................................................................................................ Section 33.6: Error conditions 232 ................................................................................................................................... Section 33.7: Clearing storage 232 ................................................................................................................................. Section 33.8: Remove Storage Item 232 ........................................................................................................................ Chapter 34: Data attributes 233 ...............................................................................................................................

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Section 34.1: Accessing data attributes 233 ................................................................................................................... Chapter 35: JSON 234 ..................................................................................................................................................... Section 35.1: JSON versus JavaScript literals 234 ......................................................................................................... Section 35.2: Parsing with a reviver function 235 ......................................................................................................... Section 35.3: Serializing a value 236 ............................................................................................................................... Section 35.4: Serializing and restoring class instances 237 ......................................................................................... Section 35.5: Serializing with a replacer function 238 .................................................................................................. Section 35.6: Parsing a simple JSON string 239 ............................................................................................................ Section 35.7: Cyclic object values 239 ............................................................................................................................ Chapter 36: AJAX 240 ...................................................................................................................................................... Section 36.1: Sending and Receiving JSON Data via POST 240 .................................................................................. Section 36.2: Add an AJAX preloader 240 ..................................................................................................................... Section 36.3: Displaying the top JavaScript questions of the month from Stack Overflow's API 241 .................... Section 36.4: Using GET with parameters 242 ............................................................................................................... Section 36.5: Check if a file exists via a HEAD request 243 .......................................................................................... Section 36.6: Using GET and no parameters 243 .......................................................................................................... Section 36.7: Listening to AJAX events at a global level 243 ....................................................................................... Chapter 37: Enumerations 244 ................................................................................................................................... Section 37.1: Enum definition using Object.freeze() 244 ............................................................................................... Section 37.2: Alternate definition 244 ............................................................................................................................. Section 37.3: Printing an enum variable 244 ................................................................................................................. Section 37.4: Implementing Enums Using Symbols 245 ............................................................................................... Section 37.5: Automatic Enumeration Value 245 .......................................................................................................... Chapter 38: Map 247 ........................................................................................................................................................ Section 38.1: Creating a Map 247 .................................................................................................................................... Section 38.2: Clearing a Map 247 ................................................................................................................................... Section 38.3: Removing an element from a Map 247 .................................................................................................. Section 38.4: Checking if a key exists in a Map 248 ...................................................................................................... Section 38.5: Iterating Maps 248 ..................................................................................................................................... Section 38.6: Getting and setting elements 248 ............................................................................................................ Section 38.7: Getting the number of elements of a Map 249 ...................................................................................... Chapter 39: Timestamps 250 ....................................................................................................................................... Section 39.1: High-resolution timestamps 250 ............................................................................................................... Section 39.2: Get Timestamp in Seconds 250 ................................................................................................................ Section 39.3: Low-resolution timestamps 250 ............................................................................................................... Section 39.4: Support for legacy browsers 250 ............................................................................................................. Chapter 40: Unary Operators 251 ........................................................................................................................... Section 40.1: Overview 251 .............................................................................................................................................. Section 40.2: The typeof operator 251 .......................................................................................................................... Section 40.3: The delete operator 252 ........................................................................................................................... Section 40.4: The unary plus operator (+) 253 .............................................................................................................. Section 40.5: The void operator 254 .............................................................................................................................. Section 40.6: The unary negation operator (-) 255 ...................................................................................................... Section 40.7: The bitwise NOT operator (~) 255 ............................................................................................................ Section 40.8: The logical NOT operator (!) 256 ............................................................................................................. Chapter 41: Generators 258 ......................................................................................................................................... Section 41.1: Generator Functions 258 ............................................................................................................................ Section 41.2: Sending Values to Generator 259 ............................................................................................................. Section 41.3: Delegating to other Generator 259 ..........................................................................................................

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Section 41.4: Iteration 259 ................................................................................................................................................ Section 41.5: Async flow with generators 260 ................................................................................................................ Section 41.6: Iterator-Observer interface 261 ................................................................................................................ Chapter 42: Promises 263 ............................................................................................................................................. Section 42.1: Introduction 263 .......................................................................................................................................... Section 42.2: Promise chaining 264 ................................................................................................................................ Section 42.3: Waiting for multiple concurrent promises 265 ....................................................................................... Section 42.4: Reduce an array to chained promises 266 ............................................................................................ Section 42.5: Waiting for the first of multiple concurrent promises 267 .................................................................... Section 42.6: "Promisifying" functions with callbacks 268 ........................................................................................... Section 42.7: Error Handling 268 .................................................................................................................................... Section 42.8: Reconciling synchronous and asynchronous operations 272 .............................................................. Section 42.9: Delay function call 273 .............................................................................................................................. Section 42.10: "Promisifying" values 273 ........................................................................................................................ Section 42.11: Using ES2017 async/await 274 ................................................................................................................ Section 42.12: Performing cleanup with finally() 274 .................................................................................................... Section 42.13: forEach with promises 275 ...................................................................................................................... Section 42.14: Asynchronous API request 275 ............................................................................................................... Chapter 43: Set 277 .......................................................................................................................................................... Section 43.1: Creating a Set 277 ...................................................................................................................................... Section 43.2: Adding a value to a Set 277 ..................................................................................................................... Section 43.3: Removing value from a set 277 ............................................................................................................... Section 43.4: Checking if a value exist in a set 278 ....................................................................................................... Section 43.5: Clearing a Set 278 ...................................................................................................................................... Section 43.6: Getting set length 278 ............................................................................................................................... Section 43.7: Converting Sets to arrays 278 .................................................................................................................. Section 43.8: Intersection and dierence in Sets 279 ................................................................................................... Section 43.9: Iterating Sets 279 ....................................................................................................................................... Chapter 44: Modals - Prompts 280 .......................................................................................................................... Section 44.1: About User Prompts 280 ........................................................................................................................... Section 44.2: Persistent Prompt Modal 280 ................................................................................................................... Section 44.3: Confirm to Delete element 281 ................................................................................................................ Section 44.4: Usage of alert() 281 .................................................................................................................................. Section 44.5: Usage of prompt() 282 ............................................................................................................................. Chapter 45: execCommand and contenteditable 283 ................................................................................... Section 45.1: Listening to Changes of contenteditable 284 .......................................................................................... Section 45.2: Getting started 284 .................................................................................................................................... Section 45.3: Copy to clipboard from textarea using execCommand("copy") 285 .................................................. Section 45.4: Formatting 285 .......................................................................................................................................... Chapter 46: History 287 ................................................................................................................................................. Section 46.1: history.pushState() 287 .............................................................................................................................. Section 46.2: history.replaceState() 287 ........................................................................................................................ Section 46.3: Load a specific URL from the history list 287 ......................................................................................... Chapter 47: Navigator Object 289 ........................................................................................................................... Section 47.1: Get some basic browser data and return it as a JSON object 289 ...................................................... Chapter 48: BOM (Browser Object Model) 290 .................................................................................................. Section 48.1: Introduction 290 .......................................................................................................................................... Section 48.2: Window Object Properties 290 ................................................................................................................. Section 48.3: Window Object Methods 291 ....................................................................................................................

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Chapter 49: The Event Loop 292 ............................................................................................................................... Section 49.1: The event loop in a web browser 292 ...................................................................................................... Section 49.2: Asynchronous operations and the event loop 293 ................................................................................ Chapter 50: Strict mode 294 ....................................................................................................................................... Section 50.1: For entire scripts 294 ................................................................................................................................. Section 50.2: For functions 294 ....................................................................................................................................... Section 50.3: Changes to properties 294 ....................................................................................................................... Section 50.4: Changes to global properties 295 ........................................................................................................... Section 50.5: Duplicate Parameters 296 ........................................................................................................................ Section 50.6: Function scoping in strict mode 296 ........................................................................................................ Section 50.7: Behaviour of a function's arguments list 296 ......................................................................................... Section 50.8: Non-Simple parameter lists 297 .............................................................................................................. Chapter 51: Custom Elements 299 ............................................................................................................................ Section 51.1: Extending Native Elements 299 ................................................................................................................. Section 51.2: Registering New Elements 299 ................................................................................................................. Chapter 52: Data Manipulation 300 ......................................................................................................................... Section 52.1: Format numbers as money 300 ............................................................................................................... Section 52.2: Extract extension from file name 300 ..................................................................................................... Section 52.3: Set object property given its string name 301 ....................................................................................... Chapter 53: Binary Data 302 ....................................................................................................................................... Section 53.1: Getting binary representation of an image file 302 ............................................................................... Section 53.2: Converting between Blobs and ArrayBuers 302 ................................................................................. Section 53.3: Manipulating ArrayBuers with DataViews 303 ..................................................................................... Section 53.4: Creating a TypedArray from a Base64 string 303 ................................................................................. Section 53.5: Using TypedArrays 304 ............................................................................................................................. Section 53.6: Iterating through an arrayBuer 304 ...................................................................................................... Chapter 54: Template Literals 306 .......................................................................................................................... Section 54.1: Basic interpolation and multiline strings 306 ........................................................................................... Section 54.2: Tagged strings 306 ................................................................................................................................... Section 54.3: Raw strings 307 .......................................................................................................................................... Section 54.4: Templating HTML With Template Strings 307 ....................................................................................... Section 54.5: Introduction 308 ......................................................................................................................................... Chapter 55: Fetch 309 ..................................................................................................................................................... Section 55.1: Getting JSON data 309 .............................................................................................................................. Section 55.2: Set Request Headers 309 ......................................................................................................................... Section 55.3: POST Data 309 ........................................................................................................................................... Section 55.4: Send cookies 310 ....................................................................................................................................... Section 55.5: GlobalFetch 310 ......................................................................................................................................... Section 55.6: Using Fetch to Display Questions from the Stack Overflow API 310 ................................................... Chapter 56: Scope 311 .................................................................................................................................................... Section 56.1: Closures 311 ................................................................................................................................................ Section 56.2: Hoisting 312 ................................................................................................................................................ Section 56.3: Dierence between var and let 315 ........................................................................................................ Section 56.4: Apply and Call syntax and invocation 317 ............................................................................................. Section 56.5: Arrow function invocation 318 ................................................................................................................. Section 56.6: Bound invocation 319 ................................................................................................................................ Section 56.7: Method invocation 319 .............................................................................................................................. Section 56.8: Anonymous invocation 320 ...................................................................................................................... Section 56.9: Constructor invocation 320 ......................................................................................................................

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Section 56.10: Using let in loops instead of var (click handlers example) 320 ........................................................... Chapter 57: Modules 322 ............................................................................................................................................... Section 57.1: Defining a module 322 ............................................................................................................................... Section 57.2: Default exports 322 ................................................................................................................................... Section 57.3: Importing named members from another module 323 ........................................................................ Section 57.4: Importing an entire module 323 .............................................................................................................. Section 57.5: Importing named members with aliases 324 ......................................................................................... Section 57.6: Importing with side eects 324 ................................................................................................................ Section 57.7: Exporting multiple named members 324 ................................................................................................ Chapter 58: Screen 325 .................................................................................................................................................. Section 58.1: Getting the screen resolution 325 ............................................................................................................. Section 58.2: Getting the “available” area of the screen 325 ...................................................................................... Section 58.3: Page width and height 325 ....................................................................................................................... Section 58.4: Window innerWidth and innerHeight Properties 325 ............................................................................ Section 58.5: Getting color information about the screen 325 .................................................................................... Chapter 59: Variable coercion/conversion 326 ................................................................................................. Section 59.1: Double Negation (!!x) 326 .......................................................................................................................... Section 59.2: Implicit conversion 326 ............................................................................................................................. Section 59.3: Converting to boolean 326 ....................................................................................................................... Section 59.4: Converting a string to a number 327 ...................................................................................................... Section 59.5: Converting a number to a string 328 ...................................................................................................... Section 59.6: Primitive to Primitive conversion table 328 ............................................................................................. Section 59.7: Convert an array to a string 328 ............................................................................................................. Section 59.8: Array to String using array methods 329 ............................................................................................... Section 59.9: Converting a number to a boolean 329 .................................................................................................. Section 59.10: Converting a string to a boolean 329 .................................................................................................... Section 59.11: Integer to Float 329 ................................................................................................................................... Section 59.12: Float to Integer 330 .................................................................................................................................. Section 59.13: Convert string to float 330 ....................................................................................................................... Chapter 60: Destructuring assignment 331 ......................................................................................................... Section 60.1: Destructuring Objects 331 ......................................................................................................................... Section 60.2: Destructuring function arguments 332 ................................................................................................... Section 60.3: Nested Destructuring 332 ......................................................................................................................... Section 60.4: Destructuring Arrays 333 .......................................................................................................................... Section 60.5: Destructuring inside variables 333 .......................................................................................................... Section 60.6: Default Value While Destructuring 334 ................................................................................................... Section 60.7: Renaming Variables While Destructuring 334 ........................................................................................ Chapter 61: WebSockets 335 ....................................................................................................................................... Section 61.1: Working with string messages 335 ........................................................................................................... Section 61.2: Establish a web socket connection 335 ................................................................................................... Section 61.3: Working with binary messages 335 ......................................................................................................... Section 61.4: Making a secure web socket connection 336 ......................................................................................... Chapter 62: Arrow Functions 337 .............................................................................................................................. Section 62.1: Introduction 337 .......................................................................................................................................... Section 62.2: Lexical Scoping & Binding (Value of "this") 337 ..................................................................................... Section 62.3: Arguments Object 338 .............................................................................................................................. Section 62.4: Implicit Return 338 ..................................................................................................................................... Section 62.5: Arrow functions as a constructor 339 ..................................................................................................... Section 62.6: Explicit Return 339 .....................................................................................................................................

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Chapter 63: Workers 340 ............................................................................................................................................... Section 63.1: Web Worker 340 ......................................................................................................................................... Section 63.2: A simple service worker 340 ..................................................................................................................... Section 63.3: Register a service worker 341 .................................................................................................................. Section 63.4: Communicating with a Web Worker 341 ................................................................................................ Section 63.5: Terminate a worker 342 ............................................................................................................................ Section 63.6: Populating your cache 343 ....................................................................................................................... Section 63.7: Dedicated Workers and Shared Workers 343 ........................................................................................ Chapter 64: requestAnimationFrame 345 ............................................................................................................ Section 64.1: Use requestAnimationFrame to fade in element 345 ............................................................................ Section 64.2: Keeping Compatibility 346 ....................................................................................................................... Section 64.3: Cancelling an Animation 346 .................................................................................................................... Chapter 65: Creational Design Patterns 348 ....................................................................................................... Section 65.1: Factory Functions 348 ................................................................................................................................ Section 65.2: Factory with Composition 349 .................................................................................................................. Section 65.3: Module and Revealing Module Patterns 350 .......................................................................................... Section 65.4: Prototype Pattern 352 ............................................................................................................................... Section 65.5: Singleton Pattern 353 ................................................................................................................................ Section 65.6: Abstract Factory Pattern 354 ................................................................................................................... Chapter 66: Detecting browser 355 ......................................................................................................................... Section 66.1: Feature Detection Method 355 ................................................................................................................. Section 66.2: User Agent Detection 355 ......................................................................................................................... Section 66.3: Library Method 356 ................................................................................................................................... Chapter 67: Symbols 357 ............................................................................................................................................... Section 67.1: Basics of symbol primitive type 357 ......................................................................................................... Section 67.2: Using Symbol.for() to create global, shared symbols 357 .................................................................... Section 67.3: Converting a symbol into a string 357 .................................................................................................... Chapter 68: Transpiling 359 ......................................................................................................................................... Section 68.1: Introduction to Transpiling 359 ................................................................................................................. Section 68.2: Start using ES6/7 with Babel 360 ............................................................................................................. Chapter 69: Automatic Semicolon Insertion - ASI 361 .................................................................................... Section 69.1: Avoid semicolon insertion on return statements 361 ............................................................................. Section 69.2: Rules of Automatic Semicolon Insertion 361 .......................................................................................... Section 69.3: Statements aected by automatic semicolon insertion 362 ................................................................ Chapter 70: Localization 364 ....................................................................................................................................... Section 70.1: Number formatting 364 ............................................................................................................................. Section 70.2: Currency formatting 364 .......................................................................................................................... Section 70.3: Date and time formatting 364 .................................................................................................................. Chapter 71: Geolocation 365 ........................................................................................................................................ Section 71.1: Get updates when a user's location changes 365 ................................................................................... Section 71.2: Get a user's latitude and longitude 365 ................................................................................................... Section 71.3: More descriptive error codes 365 ............................................................................................................. Chapter 72: IndexedDB 367 .......................................................................................................................................... Section 72.1: Opening a database 367 ........................................................................................................................... Section 72.2: Adding objects 367 .................................................................................................................................... Section 72.3: Retrieving data 368 ................................................................................................................................... Section 72.4: Testing for IndexedDB availability 369 .................................................................................................... Chapter 73: Modularization Techniques 370 ....................................................................................................... Section 73.1: ES6 Modules 370 .........................................................................................................................................

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Section 73.2: Universal Module Definition (UMD) 370 .................................................................................................. Section 73.3: Immediately invoked function expressions (IIFE) 371 ............................................................................ Section 73.4: Asynchronous Module Definition (AMD) 371 .......................................................................................... Section 73.5: CommonJS - Node.js 372 .......................................................................................................................... Chapter 74: Proxy 374 .................................................................................................................................................... Section 74.1: Proxying property lookup 374 .................................................................................................................. Section 74.2: Very simple proxy (using the set trap) 374 ............................................................................................ Chapter 75: .postMessage() and MessageEvent 376 ...................................................................................... Section 75.1: Getting Started 376 .................................................................................................................................... Chapter 76: WeakMap 379 ............................................................................................................................................ Section 76.1: Creating a WeakMap object 379 .............................................................................................................. Section 76.2: Getting a value associated to the key 379 .............................................................................................. Section 76.3: Assigning a value to the key 379 ............................................................................................................. Section 76.4: Checking if an element with the key exists 379 ...................................................................................... Section 76.5: Removing an element with the key 380 .................................................................................................. Section 76.6: Weak reference demo 380 ....................................................................................................................... Chapter 77: WeakSet 382 .............................................................................................................................................. Section 77.1: Creating a WeakSet object 382 ................................................................................................................ Section 77.2: Adding a value 382 .................................................................................................................................... Section 77.3: Checking if a value exists 382 ................................................................................................................... Section 77.4: Removing a value 382 ............................................................................................................................... Chapter 78: Escape Sequences 383 ......................................................................................................................... Section 78.1: Entering special characters in strings and regular expressions 383 .................................................... Section 78.2: Escape sequence types 383 ..................................................................................................................... Chapter 79: Behavioral Design Patterns 386 ...................................................................................................... Section 79.1: Observer pattern 386 ................................................................................................................................. Section 79.2: Mediator Pattern 387 ................................................................................................................................ Section 79.3: Command 388 ............................................................................................................................................ Section 79.4: Iterator 389 ................................................................................................................................................. Chapter 80: Server-sent events 391 ........................................................................................................................ Section 80.1: Setting up a basic event stream to the server 391 ................................................................................. Section 80.2: Closing an event stream 391 ................................................................................................................... Section 80.3: Binding event listeners to EventSource 391 ........................................................................................... Chapter 81: Async functions (async/await) 393 ................................................................................................ Section 81.1: Introduction 393 .......................................................................................................................................... Section 81.2: Await and operator precedence 393 ....................................................................................................... Section 81.3: Async functions compared to Promises 394 ........................................................................................... Section 81.4: Looping with async await 395 ................................................................................................................... Section 81.5: Less indentation 396 .................................................................................................................................. Section 81.6: Simultaneous async (parallel) operations 397 ........................................................................................ Chapter 82: Async Iterators 398 ................................................................................................................................ Section 82.1: Basics 398 ................................................................................................................................................... Chapter 83: How to make iterator usable inside async callback function 399 ................................. Section 83.1: Erroneous code, can you spot why this usage of key will lead to bugs? 399 ...................................... Section 83.2: Correct Writing 399 ................................................................................................................................... Chapter 84: Tail Call Optimization 400 .................................................................................................................. Section 84.1: What is Tail Call Optimization (TCO) 400 ................................................................................................ Section 84.2: Recursive loops 400 ..................................................................................................................................

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Chapter 85: Bitwise Operators - Real World Examples (snippets) 401 ................................................. Section 85.1: Swapping Two Integers with Bitwise XOR (without additional memory allocation) 401 .................... Section 85.2: Faster multiplication or division by powers of 2 401 ............................................................................. Section 85.3: Number's Parity Detection with Bitwise AND 401 .................................................................................. Chapter 86: Tilde ~ 403 ................................................................................................................................................... Section 86.1: ~ Integer 403 ............................................................................................................................................... Section 86.2: ~~ Operator 403 ......................................................................................................................................... Section 86.3: Converting Non-numeric values to Numbers 404 .................................................................................. Section 86.4: Shorthands 404 .......................................................................................................................................... Section 86.5: ~ Decimal 404 ............................................................................................................................................. Chapter 87: Using JavaScript to get/set CSS custom variables 406 ..................................................... Section 87.1: How to get and set CSS variable property values 406 ........................................................................... Chapter 88: Selection API 407 ..................................................................................................................................... Section 88.1: Get the text of the selection 407 ............................................................................................................... Section 88.2: Deselect everything that is selected 407 ................................................................................................ Section 88.3: Select the contents of an element 407 .................................................................................................... Chapter 89: File API, Blobs and FileReaders 408 ............................................................................................... Section 89.1: Read file as string 408 ............................................................................................................................... Section 89.2: Read file as dataURL 408 ......................................................................................................................... Section 89.3: Slice a file 409 ............................................................................................................................................. Section 89.4: Get the properties of the file 409 ............................................................................................................. Section 89.5: Selecting multiple files and restricting file types 410 ............................................................................. Section 89.6: Client side csv download using Blob 410 ................................................................................................ Chapter 90: Notifications API 411 ............................................................................................................................. Section 90.1: Requesting Permission to send notifications 411 ................................................................................... Section 90.2: Sending Notifications 411 ......................................................................................................................... Section 90.3: Closing a notification 411 ......................................................................................................................... Section 90.4: Notification events 412 ............................................................................................................................. Chapter 91: Vibration API 413 ...................................................................................................................................... Section 91.1: Single vibration 413 ..................................................................................................................................... Section 91.2: Check for support 413 ............................................................................................................................... Section 91.3: Vibration patterns 413 ............................................................................................................................... Chapter 92: Battery Status API 414 ......................................................................................................................... Section 92.1: Battery Events 414 ..................................................................................................................................... Section 92.2: Getting current battery level 414 ............................................................................................................. Section 92.3: Is battery charging? 414 ........................................................................................................................... Section 92.4: Get time left until battery is empty 414 ................................................................................................... Section 92.5: Get time left until battery is fully charged 414 ....................................................................................... Chapter 93: Fluent API 415 ............................................................................................................................................ Section 93.1: Fluent API capturing construction of HTML articles with JS 415 ........................................................... Chapter 94: Web Cryptography API 417 ............................................................................................................... Section 94.1: Creating digests (e.g. SHA-256) 417 ......................................................................................................... Section 94.2: Cryptographically random data 417 ....................................................................................................... Section 94.3: Generating RSA key pair and converting to PEM format 418 .............................................................. Section 94.4: Converting PEM key pair to CryptoKey 419 ........................................................................................... Chapter 95: Security issues 421 ................................................................................................................................. Section 95.1: Reflected Cross-site scripting (XSS) 421 .................................................................................................. Section 95.2: Persistent Cross-site scripting (XSS) 422 ................................................................................................ Section 95.3: Persistent Cross-site scripting from JavaScript string literals 423 .......................................................

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Section 95.4: Why scripts from other people can harm your website and its visitors 423 ...................................... Section 95.5: Evaled JSON injection 424 ........................................................................................................................ Chapter 96: Same Origin Policy & Cross-Origin Communication 426 ..................................................... Section 96.1: Safe cross-origin communication with messages 426 ........................................................................... Section 96.2: Ways to circumvent Same-Origin Policy 427 ......................................................................................... Chapter 97: Error Handling 429 ................................................................................................................................. Section 97.1: Error objects 429 ........................................................................................................................................ Section 97.2: Interaction with Promises 429 .................................................................................................................. Section 97.3: Error types 430 ........................................................................................................................................... Section 97.4: Order of operations plus advanced thoughts 430 ................................................................................. Chapter 98: Global error handling in browsers 433 ........................................................................................ Section 98.1: Handling window.onerror to report all errors back to the server-side 433 ......................................... Chapter 99: Debugging 435 .......................................................................................................................................... Section 99.1: Interactive interpreter variables 435 ........................................................................................................ Section 99.2: Breakpoints 435 ......................................................................................................................................... Section 99.3: Using setters and getters to find what changed a property 436 ......................................................... Section 99.4: Using the console 437 ............................................................................................................................... Section 99.5: Automatically pausing execution 438 ..................................................................................................... Section 99.6: Elements inspector 438 ............................................................................................................................. Section 99.7: Break when a function is called 438 ........................................................................................................ Section 99.8: Stepping through code 439 ...................................................................................................................... Chapter 100: Unit Testing JavaScript 440 ............................................................................................................ Section 100.1: Unit Testing Promises with Mocha, Sinon, Chai and Proxyquire 440 ................................................... Section 100.2: Basic Assertion 442 .................................................................................................................................. Chapter 101: Evaluating JavaScript 444 ................................................................................................................ Section 101.1: Evaluate a string of JavaScript statements 444 .................................................................................... Section 101.2: Introduction 444 ........................................................................................................................................ Section 101.3: Evaluation and Math 444 .......................................................................................................................... Chapter 102: Linters - Ensuring code quality 445 ............................................................................................. Section 102.1: JSHint 445 .................................................................................................................................................. Section 102.2: ESLint / JSCS 446 ..................................................................................................................................... Section 102.3: JSLint 446 .................................................................................................................................................. Chapter 103: Anti-patterns 447 .................................................................................................................................. Section 103.1: Chaining assignments in var declarations 447 ...................................................................................... Chapter 104: Performance Tips 448 ........................................................................................................................ Section 104.1: Avoid try/catch in performance-critical functions 448 ......................................................................... Section 104.2: Limit DOM Updates 448 ........................................................................................................................... Section 104.3: Benchmarking your code - measuring execution time 449 ................................................................ Section 104.4: Use a memoizer for heavy-computing functions 451 ......................................................................... Section 104.5: Initializing object properties with null 453 .............................................................................................. Section 104.6: Reuse objects rather than recreate 454 ................................................................................................ Section 104.7: Prefer local variables to globals, attributes, and indexed values 455 ................................................ Section 104.8: Be consistent in use of Numbers 456 ..................................................................................................... Chapter 105: Memory eciency 458 ....................................................................................................................... Section 105.1: Drawback of creating true private method 458 .................................................................................... Appendix A: Reserved Keywords 459 ...................................................................................................................... Section A.1: Reserved Keywords 459 .............................................................................................................................. Section A.2: Identifiers & Identifier Names 461 .............................................................................................................

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Credits 463 ............................................................................................................................................................................ You may also like 474 ......................................................................................................................................................

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GoalKicker.com – JavaScript® Notes for Professionals 1 About Please feel free to share this PDF with anyone for free, latest version of this book can be downloaded from: https://goalkicker.com/JavaScriptBook This JavaScript® Notes for Professionals book is compiled from Stack Overflow Documentation, the content is written by the beautiful people at Stack Overflow. Text content is released under Creative Commons BY-SA, see credits at the end of this book whom contributed to the various chapters. Images may be copyright of their respective owners unless otherwise specified This is an unofficial free book created for educational purposes and is not affiliated with official JavaScript® group(s) or company(s) nor Stack Overflow. All trademarks and registered trademarks are the property of their respective company owners The information presented in this book is not guaranteed to be correct nor accurate, use at your own risk Please send feedback and corrections to web@petercv.com

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GoalKicker.com – JavaScript® Notes for Professionals 2 Chapter 1: Getting started with JavaScript Version Release Date 1 1997-06-01 2 1998-06-01 3 1998-12-01 E4X 2004-06-01 5 2009-12-01 5.1 2011-06-01 6 2015-06-01 7 2016-06-14 8 2017-06-27 Section 1.1: Using console.log() Introduction All modern web browsers, Node.js as well as almost every other JavaScript environments support writing messages to a console using a suite of logging methods. The most common of these methods is console.log(). In a browser environment, the console.log() function is predominantly used for debugging purposes. Getting Started Open up the JavaScript Console in your browser, type the following, and press Enter : console.log("Hello, World!"); This will log the following to the console: In the example above, the console.log() function prints Hello, World! to the console and returns undefined (shown above in the console output window). This is because console.log() has no explicit return value. Logging variables console.log() can be used to log variables of any kind; not only strings. Just pass in the variable that you want to be displayed in the console, for example: var foo = "bar"; console.log(foo); This will log the following to the console:

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GoalKicker.com – JavaScript® Notes for Professionals 3 If you want to log two or more values, simply separate them with commas. Spaces will be automatically added between each argument during concatenation: var thisVar = 'first value'; var thatVar = 'second value'; console.log("thisVar:", thisVar, "and thatVar:", thatVar); This will log the following to the console: Placeholders You can use console.log() in combination with placeholders: var greet = "Hello", who = "World"; console.log("%s, %s!", greet, who); This will log the following to the console: Logging Objects Below we see the result of logging an object. This is often useful for logging JSON responses from API calls. console.log({ 'Email': '', 'Groups': {}, 'Id': 33, 'IsHiddenInUI': false, 'IsSiteAdmin': false, 'LoginName': 'i:0#.w|virtualdomain\\user2', 'PrincipalType': 1,

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GoalKicker.com – JavaScript® Notes for Professionals 4 'Title': 'user2' }); This will log the following to the console: Logging HTML elements You have the ability to log any element which exists within the DOM. In this case we log the body element: console.log(document.body); This will log the following to the console: End Note For more information on the capabilities of the console, see the Console topic. Section 1.2: Using the DOM API DOM stands for Document Object Model. It is an object-oriented representation of structured documents like XML and HTML. Setting the textContent property of an Element is one way to output text on a web page. For example, consider the following HTML tag: <p id="paragraph"></p> To change its textContent property, we can run the following JavaScript: