book

JavaScript: The Definitive Guide, 7th Edition

by David Flanagan

May 2020

Intermediate to advanced

706 pages

21h 15m

English

O'Reilly Media, Inc.

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Conventions Used in This BookExample CodeO’Reilly Online LearningHow to Contact UsAcknowledgments
1.1 Exploring JavaScript1.2 Hello World1.3 A Tour of JavaScript1.4 Example: Character Frequency Histograms1.5 Summary
2.1 The Text of a JavaScript Program2.2 Comments2.3 Literals2.4 Identifiers and Reserved Words2.4.1 Reserved Words2.5 Unicode2.5.1 Unicode Escape Sequences2.5.2 Unicode Normalization2.6 Optional Semicolons2.7 Summary
3.1 Overview and Definitions3.2 Numbers3.2.1 Integer Literals3.2.2 Floating-Point Literals3.2.3 Arithmetic in JavaScript3.2.4 Binary Floating-Point and Rounding Errors3.2.5 Arbitrary Precision Integers with BigInt3.2.6 Dates and Times3.3 Text3.3.1 String Literals3.3.2 Escape Sequences in String Literals3.3.3 Working with Strings3.3.4 Template Literals3.3.5 Pattern Matching3.4 Boolean Values3.5 null and undefined3.6 Symbols3.7 The Global Object3.8 Immutable Primitive Values and Mutable Object References3.9 Type Conversions3.9.1 Conversions and Equality3.9.2 Explicit Conversions3.9.3 Object to Primitive Conversions3.10 Variable Declaration and Assignment3.10.1 Declarations with let and const3.10.2 Variable Declarations with var3.10.3 Destructuring Assignment3.11 Summary
4.1 Primary Expressions4.2 Object and Array Initializers4.3 Function Definition Expressions4.4 Property Access Expressions4.4.1 Conditional Property Access4.5 Invocation Expressions4.5.1 Conditional Invocation4.6 Object Creation Expressions4.7 Operator Overview4.7.1 Number of Operands4.7.2 Operand and Result Type4.7.3 Operator Side Effects4.7.4 Operator Precedence4.7.5 Operator Associativity4.7.6 Order of Evaluation4.8 Arithmetic Expressions4.8.1 The + Operator4.8.2 Unary Arithmetic Operators4.8.3 Bitwise Operators4.9 Relational Expressions4.9.1 Equality and Inequality Operators4.9.2 Comparison Operators4.9.3 The in Operator4.9.4 The instanceof Operator4.10 Logical Expressions4.10.1 Logical AND (&&)4.10.2 Logical OR (||)4.10.3 Logical NOT (!)4.11 Assignment Expressions4.11.1 Assignment with Operation4.12 Evaluation Expressions4.12.1 eval()4.12.2 Global eval()4.12.3 Strict eval()4.13 Miscellaneous Operators4.13.1 The Conditional Operator (?:)4.13.2 First-Defined (??)4.13.3 The typeof Operator4.13.4 The delete Operator4.13.5 The await Operator4.13.6 The void Operator4.13.7 The comma Operator (,)4.14 Summary
5.1 Expression Statements5.2 Compound and Empty Statements5.3 Conditionals5.3.1 if5.3.2 else if5.3.3 switch5.4 Loops5.4.1 while5.4.2 do/while5.4.3 for5.4.4 for/of5.4.5 for/in5.5 Jumps5.5.1 Labeled Statements5.5.2 break5.5.3 continue5.5.4 return5.5.5 yield5.5.6 throw5.5.7 try/catch/finally5.6 Miscellaneous Statements5.6.1 with5.6.2 debugger5.6.3 “use strict”5.7 Declarations5.7.1 const, let, and var5.7.2 function5.7.3 class5.7.4 import and export5.8 Summary of JavaScript Statements
6.1 Introduction to Objects6.2 Creating Objects6.2.1 Object Literals6.2.2 Creating Objects with new6.2.3 Prototypes6.2.4 Object.create()6.3 Querying and Setting Properties6.3.1 Objects As Associative Arrays6.3.2 Inheritance6.3.3 Property Access Errors6.4 Deleting Properties6.5 Testing Properties6.6 Enumerating Properties6.6.1 Property Enumeration Order6.7 Extending Objects6.8 Serializing Objects6.9 Object Methods6.9.1 The toString() Method6.9.2 The toLocaleString() Method6.9.3 The valueOf() Method6.9.4 The toJSON() Method6.10 Extended Object Literal Syntax6.10.1 Shorthand Properties6.10.2 Computed Property Names6.10.3 Symbols as Property Names6.10.4 Spread Operator6.10.5 Shorthand Methods6.10.6 Property Getters and Setters6.11 Summary
7.1 Creating Arrays7.1.1 Array Literals7.1.2 The Spread Operator7.1.3 The Array() Constructor7.1.4 Array.of()7.1.5 Array.from()7.2 Reading and Writing Array Elements7.3 Sparse Arrays7.4 Array Length7.5 Adding and Deleting Array Elements7.6 Iterating Arrays7.7 Multidimensional Arrays7.8 Array Methods7.8.1 Array Iterator Methods7.8.2 Flattening arrays with flat() and flatMap()7.8.3 Adding arrays with concat()7.8.4 Stacks and Queues with push(), pop(), shift(), and unshift()7.8.5 Subarrays with slice(), splice(), fill(), and copyWithin()7.8.6 Array Searching and Sorting Methods7.8.7 Array to String Conversions7.8.8 Static Array Functions7.9 Array-Like Objects7.10 Strings as Arrays7.11 Summary
8.1 Defining Functions8.1.1 Function Declarations8.1.2 Function Expressions8.1.3 Arrow Functions8.1.4 Nested Functions8.2 Invoking Functions8.2.1 Function Invocation8.2.2 Method Invocation8.2.3 Constructor Invocation8.2.4 Indirect Invocation8.2.5 Implicit Function Invocation8.3 Function Arguments and Parameters8.3.1 Optional Parameters and Defaults8.3.2 Rest Parameters and Variable-Length Argument Lists8.3.3 The Arguments Object8.3.4 The Spread Operator for Function Calls8.3.5 Destructuring Function Arguments into Parameters8.3.6 Argument Types8.4 Functions as Values8.4.1 Defining Your Own Function Properties8.5 Functions as Namespaces8.6 Closures8.7 Function Properties, Methods, and Constructor8.7.1 The length Property8.7.2 The name Property8.7.3 The prototype Property8.7.4 The call() and apply() Methods8.7.5 The bind() Method8.7.6 The toString() Method8.7.7 The Function() Constructor8.8 Functional Programming8.8.1 Processing Arrays with Functions8.8.2 Higher-Order Functions8.8.3 Partial Application of Functions8.8.4 Memoization8.9 Summary
9.1 Classes and Prototypes9.2 Classes and Constructors9.2.1 Constructors, Class Identity, and instanceof9.2.2 The constructor Property9.3 Classes with the class Keyword9.3.1 Static Methods9.3.2 Getters, Setters, and other Method Forms9.3.3 Public, Private, and Static Fields9.3.4 Example: A Complex Number Class9.4 Adding Methods to Existing Classes9.5 Subclasses9.5.1 Subclasses and Prototypes9.5.2 Subclasses with extends and super9.5.3 Delegation Instead of Inheritance9.5.4 Class Hierarchies and Abstract Classes9.6 Summary

10.1 Modules with Classes, Objects, and Closures10.1.1 Automating Closure-Based Modularity10.2 Modules in Node10.2.1 Node Exports10.2.2 Node Imports10.2.3 Node-Style Modules on the Web10.3 Modules in ES610.3.1 ES6 Exports10.3.2 ES6 Imports10.3.3 Imports and Exports with Renaming10.3.4 Re-Exports10.3.5 JavaScript Modules on the Web10.3.6 Dynamic Imports with import()10.3.7 import.meta.url10.4 Summary
11.1 Sets and Maps11.1.1 The Set Class11.1.2 The Map Class11.1.3 WeakMap and WeakSet11.2 Typed Arrays and Binary Data11.2.1 Typed Array Types11.2.2 Creating Typed Arrays11.2.3 Using Typed Arrays11.2.4 Typed Array Methods and Properties11.2.5 DataView and Endianness11.3 Pattern Matching with Regular Expressions11.3.1 Defining Regular Expressions11.3.2 String Methods for Pattern Matching11.3.3 The RegExp Class11.4 Dates and Times11.4.1 Timestamps11.4.2 Date Arithmetic11.4.3 Formatting and Parsing Date Strings11.5 Error Classes11.6 JSON Serialization and Parsing11.6.1 JSON Customizations11.7 The Internationalization API11.7.1 Formatting Numbers11.7.2 Formatting Dates and Times11.7.3 Comparing Strings11.8 The Console API11.8.1 Formatted Output with Console11.9 URL APIs11.9.1 Legacy URL Functions11.10 Timers11.11 Summary
12.1 How Iterators Work12.2 Implementing Iterable Objects12.2.1 “Closing” an Iterator: The Return Method12.3 Generators12.3.1 Generator Examples12.3.2 yield* and Recursive Generators12.4 Advanced Generator Features12.4.1 The Return Value of a Generator Function12.4.2 The Value of a yield Expression12.4.3 The return() and throw() Methods of a Generator12.4.4 A Final Note About Generators12.5 Summary
13.1 Asynchronous Programming with Callbacks13.1.1 Timers13.1.2 Events13.1.3 Network Events13.1.4 Callbacks and Events in Node13.2 Promises13.2.1 Using Promises13.2.2 Chaining Promises13.2.3 Resolving Promises13.2.4 More on Promises and Errors13.2.5 Promises in Parallel13.2.6 Making Promises13.2.7 Promises in Sequence13.3 async and await13.3.1 await Expressions13.3.2 async Functions13.3.3 Awaiting Multiple Promises13.3.4 Implementation Details13.4 Asynchronous Iteration13.4.1 The for/await Loop13.4.2 Asynchronous Iterators13.4.3 Asynchronous Generators13.4.4 Implementing Asynchronous Iterators13.5 Summary
14.1 Property Attributes14.2 Object Extensibility14.3 The prototype Attribute14.4 Well-Known Symbols14.4.1 Symbol.iterator and Symbol.asyncIterator14.4.2 Symbol.hasInstance14.4.3 Symbol.toStringTag14.4.4 Symbol.species14.4.5 Symbol.isConcatSpreadable14.4.6 Pattern-Matching Symbols14.4.7 Symbol.toPrimitive14.4.8 Symbol.unscopables14.5 Template Tags14.6 The Reflect API14.7 Proxy Objects14.7.1 Proxy Invariants14.8 Summary
15.1 Web Programming Basics15.1.1 JavaScript in HTML <script> Tags15.1.2 The Document Object Model15.1.3 The Global Object in Web Browsers15.1.4 Scripts Share a Namespace15.1.5 Execution of JavaScript Programs15.1.6 Program Input and Output15.1.7 Program Errors15.1.8 The Web Security Model15.2 Events15.2.1 Event Categories15.2.2 Registering Event Handlers15.2.3 Event Handler Invocation15.2.4 Event Propagation15.2.5 Event Cancellation15.2.6 Dispatching Custom Events15.3 Scripting Documents15.3.1 Selecting Document Elements15.3.2 Document Structure and Traversal15.3.3 Attributes15.3.4 Element Content15.3.5 Creating, Inserting, and Deleting Nodes15.3.6 Example: Generating a Table of Contents15.4 Scripting CSS15.4.1 CSS Classes15.4.2 Inline Styles15.4.3 Computed Styles15.4.4 Scripting Stylesheets15.4.5 CSS Animations and Events15.5 Document Geometry and Scrolling15.5.1 Document Coordinates and Viewport Coordinates15.5.2 Querying the Geometry of an Element15.5.3 Determining the Element at a Point15.5.4 Scrolling15.5.5 Viewport Size, Content Size, and Scroll Position15.6 Web Components15.6.1 Using Web Components15.6.2 HTML Templates15.6.3 Custom Elements15.6.4 Shadow DOM15.6.5 Example: a <search-box> Web Component15.7 SVG: Scalable Vector Graphics15.7.1 SVG in HTML15.7.2 Scripting SVG15.7.3 Creating SVG Images with JavaScript15.8 Graphics in a <canvas>15.8.1 Paths and Polygons15.8.2 Canvas Dimensions and Coordinates15.8.3 Graphics Attributes15.8.4 Canvas Drawing Operations15.8.5 Coordinate System Transforms15.8.6 Clipping15.8.7 Pixel Manipulation15.9 Audio APIs15.9.1 The Audio() Constructor15.9.2 The WebAudio API15.10 Location, Navigation, and History15.10.1 Loading New Documents15.10.2 Browsing History15.10.3 History Management with hashchange Events15.10.4 History Management with pushState()15.11 Networking15.11.1 fetch()15.11.2 Server-Sent Events15.11.3 WebSockets15.12 Storage15.12.1 localStorage and sessionStorage15.12.2 Cookies15.12.3 IndexedDB15.13 Worker Threads and Messaging15.13.1 Worker Objects15.13.2 The Global Object in Workers15.13.3 Importing Code into a Worker15.13.4 Worker Execution Model15.13.5 postMessage(), MessagePorts, and MessageChannels15.13.6 Cross-Origin Messaging with postMessage()15.14 Example: The Mandelbrot Set15.15 Summary and Suggestions for Further Reading15.15.1 HTML and CSS15.15.2 Performance15.15.3 Security15.15.4 WebAssembly15.15.5 More Document and Window Features15.15.6 Events15.15.7 Progressive Web Apps and Service Workers15.15.8 Mobile Device APIs15.15.9 Binary APIs15.15.10 Media APIs15.15.11 Cryptography and Related APIs
16.1 Node Programming Basics16.1.1 Console Output16.1.2 Command-Line Arguments and Environment Variables16.1.3 Program Life Cycle16.1.4 Node Modules16.1.5 The Node Package Manager16.2 Node Is Asynchronous by Default16.3 Buffers16.4 Events and EventEmitter16.5 Streams16.5.1 Pipes16.5.2 Asynchronous Iteration16.5.3 Writing to Streams and Handling Backpressure16.5.4 Reading Streams with Events16.6 Process, CPU, and Operating System Details16.7 Working with Files16.7.1 Paths, File Descriptors, and FileHandles16.7.2 Reading Files16.7.3 Writing Files16.7.4 File Operations16.7.5 File Metadata16.7.6 Working with Directories16.8 HTTP Clients and Servers16.9 Non-HTTP Network Servers and Clients16.10 Working with Child Processes16.10.1 execSync() and execFileSync()16.10.2 exec() and execFile()16.10.3 spawn()16.10.4 fork()16.11 Worker Threads16.11.1 Creating Workers and Passing Messages16.11.2 The Worker Execution Environment16.11.3 Communication Channels and MessagePorts16.11.4 Transferring MessagePorts and Typed Arrays16.11.5 Sharing Typed Arrays Between Threads16.12 Summary
17.1 Linting with ESLint17.2 JavaScript Formatting with Prettier17.3 Unit Testing with Jest17.4 Package Management with npm17.5 Code Bundling17.6 Transpilation with Babel17.7 JSX: Markup Expressions in JavaScript17.8 Type Checking with Flow17.8.1 Installing and Running Flow17.8.2 Using Type Annotations17.8.3 Class Types17.8.4 Object Types17.8.5 Type Aliases17.8.6 Array Types17.8.7 Other Parameterized Types17.8.8 Read-Only Types17.8.9 Function Types17.8.10 Union Types17.8.11 Enumerated Types and Discriminated Unions17.9 Summary

Content preview from JavaScript: The Definitive Guide, 7th Edition

Chapter 13. Asynchronous JavaScript

Some computer programs, such as scientific simulations and machine learning models, are compute-bound: they run continuously, without pause, until they have computed their result. Most real-world computer programs, however, are significantly asynchronous. This means that they often have to stop computing while waiting for data to arrive or for some event to occur. JavaScript programs in a web browser are typically event-driven, meaning that they wait for the user to click or tap before they actually do anything. And JavaScript-based servers typically wait for client requests to arrive over the network before they do anything.

This kind of asynchronous programming is commonplace in JavaScript, and this chapter documents three important language features that help make it easier to work with asynchronous code. Promises, new in ES6, are objects that represent the not-yet-available result of an asynchronous operation. The keywords async and await were introduced in ES2017 and provide new syntax that simplifies asynchronous programming by allowing you to structure your Promise-based code as if it was synchronous. Finally, asynchronous iterators and the for/await loop were introduced in ES2018 and allow you to work with streams of asynchronous events using simple loops that appear synchronous.

Ironically, even though JavaScript provides these powerful features for working with asynchronous code, there are no features of the core language that are ...