JavaScript

HTML gives a page structure, CSS gives it style and JavaScript gives it behavior: menus, live form validation, whole single-page applications. The same language also runs servers, build tools and desktop apps.

This chapter teaches the language itself, as standardized in ECMAScript 2026: values and types, objects, functions, promises, classes and the built-in library, from strings and arrays to Intl, Proxy and regular expressions. Browser APIs such as the DOM come in HTML DOM APIs and Web APIs, and TypeScript, which adds static types on top, in TypeScript.

Every example is runnable, with output captured from a real engine: paste it into a browser console or run it with Node.js 2,131 (Node.js Quick Start).

What you will learn:

• Where JavaScript came from, how engines execute it and how new features are standardized

• Variables, types, objects, flow control, functions, asynchrony and classes

• The built-in objects: numbers, strings, arrays, typed arrays, collections, iterators, dates and more

• Memory, performance and debugging, what each ECMAScript edition added, and essential libraries

Sections

• Introduction
  • A Brief History
  • Engines and Runtimes
  • Running JavaScript
  • How V8 Executes Code
  • The TC39 Process
• Variables
  • Names
  • Values
  • Types
  • Scope
  • Export and Import
• Objects
  • Operators for Objects
  • JSON
  • Object Destructuring
  • delete
  • Methods and Namespaces
  • Shorthand Assignment Notation
  • Object Static Methods
  • Object.prototype Members
  • Copying and Comparing
  • prototype, this and new
  • Descriptors and Freezing
• Flow Control
  • Conditional Branching
  • Repetition Loops
  • Error Handling
• Functions
  • Parameters
  • Arrow Functions
  • Scoping and Hoisting
  • Timers
  • Being a Class Constructor
  • The Function Object
  • Closures
  • OOP the Classical Way
  • Generators
  • Functional Patterns
• Promises and Asynchrony
  • Callbacks and the Event Loop
  • resolve() and reject()
  • then(), catch(), finally()
  • Writing Your Own Promise
  • Macrotasks and Microtasks
  • Promise.resolve/reject()
  • Promise Combinators
  • async Functions and await
  • Asynchronous Iteration
  • Practical Asynchrony
  • withResolvers() and try()
• Classes
  • Getters and Setters
  • Inheritance
  • Generator and async Methods
  • Mixins
  • Abstract Classes
  • Private and Static Blocks
  • Static Constants
  • async Constructors
  • Object Relay
  • Command Objects
  • Decorators
• undefined and null
• Booleans
  • Truthiness
  • Boolean Prototype Methods
• Numbers
  • Number Static Properties
  • Number Static Methods
  • Number Prototype Methods
  • Number Literals
  • BigInt
  • Floating-Point Pitfalls
• Symbols
  • Non-equality
  • Accessibility
  • Well-known Symbols
  • Symbol Static Methods
  • Symbol.prototype
  • Symbols vs Private Fields
• Strings
  • Escape Notation
  • Template Literals
  • String Static Methods
  • String Prototype Methods
  • Encoding URIs
  • eval()
  • Hashbang
  • Tagged Templates
• Arrays
  • Static Properties and Methods
  • Accessor Methods
  • Mutator Methods
  • Iteration Methods
  • Destructuring Assignment
  • Rest and Spread
  • Copying Array Methods
• Typed Arrays and Binary Data
  • ArrayBuffer
  • DataView
  • SharedArrayBuffer
  • Atomics
  • Uint8Array Base64 and Hex
  • Float16Array
• Sets and Maps
  • Set and WeakSet
  • Map and WeakMap
  • WeakRef
  • FinalizationRegistry
  • Upsert Methods
• Iterables and Iterators
  • The Simplest Iterable
  • Overriding Built-in Iterables
  • User-defined Iterables
  • Generators and yield*
  • Iterator Helpers
  • Iterator.concat()
• Math
  • Static Properties
  • Static Methods
• Date
  • Static Timestamp Methods
  • Prototype Setters and Getters
  • Prototype Conversion Getters
  • Temporal
  • Date Libraries
• Regular Expressions
  • Special Characters
  • Groups and Backreferences
  • Flags
  • Prototype Properties
  • RegExp.escape()
  • Prototype Methods
• Intl
  • Collator
  • NumberFormat
  • DateTimeFormat
  • Other Intl Formatters
• Proxy and Reflect
  • Handlers for Functions
  • Handlers for Operators
  • Object.X() Handlers
• Operators
  • Precedence and Associativity
  • Ternary Operator
  • Increment and Decrement
  • Assignment Operators
  • Bitwise Operators
  • The Comma Operator
  • ?., ?? and **
• Strict Mode
  • General Restrictions
  • Restrictions on Functions
• Memory and Performance
  • Garbage Collection
  • Hidden Classes
  • Profiling and Source Maps
• Version Features
  • ES5
  • ES2015
  • ES2016
  • ES2017
  • ES2018
  • ES2019
  • ES2020
  • ES2021
  • ES2022
  • ES2023
  • ES2024
  • ES2025
  • ES2026
  • ECMAScript 2027 and Beyond
• Essential JavaScript Libraries
• Test Yourself!