Skip to content
JavaScript Book
Search
Ctrl
K
Cancel
GitHub
Select language
English
Français
1 - JavaScript Foundations
1.1 History and Evolution of JavaScript
1.2 Setting Up Your Development Environment
1.3 Your First JavaScript Program
1.4 JavaScript in Different Environments
1.5 Understanding the ECMAScript Specification
2 - Variables and Data Types
2.1 Variables: var, let, and const
2.2 Hoisting and Temporal Dead Zone
2.3 Primitive Data Types
2.3.1 Number (integers, floats, NaN, Infinity)
2.3.2 String (methods, template literals ...)
2.3.3 Boolean
2.3.4 Undefined and Null
2.3.5 Symbol
2.3.6 BigInt
2.4 Reference Data Types
2.4.1 Object
2.4.2 Array
2.4.3 Function
2.5 Type Coercion and Conversion
2.6 Type Checking Methods (typeof, instanceof,..)
3 - Operators and Expressions
3.1 Arithmetic Operators
3.2 Assignment Operators
3.3 Comparison Operators (== vs ===)
3.4 Logical Operators (&&, ||, ??)
3.5 Bitwise Operators
3.6 Ternary Operator
3.7 Comma Operator
3.8 typeof and instanceof Operators
3.9 Optional Chaining (?.)
3.10 Nullish Coalescing (??)
3.11 Operator Precedence and Associativity
4 - Control Flow
4.1 Conditional Statements
4.1.1 if, else if, else
4.1.2 switch statement
4.1.3 Conditional (ternary) operator
4.2 Loops
4.2.1 for loop
4.2.2 while loop
4.2.3 do...while loop
4.2.4 for...in loop
4.2.5 for...of loop
4.3 Loop Control (break, continue, labeled statements)
4.4 Error Handling with try/catch/finally
4.5 Throwing Custom Errors
5 - Function Fundamentals
5.1 Function Declarations
5.2 Function Expressions
5.3 Arrow Functions
5.4 Immediately Invoked Function Expressions (IIFE)
5.5 Generator Functions
5.6 Async Functions
5.7 Function Parameters
5.7.1 Default Parameters
5.7.2 Rest Parameters
5.7.3 The arguments Object
5.7.4 Parameter Destructuring
6 - The 'this' Keyword
6.1 What is 'this'?
6.2 Global Context
6.3 Function Context
6.4 Method Context
6.5 Constructor Context
6.6 Event Handler Context
6.7 Arrow Functions and 'this'
6.8 Explicit Binding
6.8.1 call()
6.8.2 apply()
6.8.3 bind()
6.9 'this' Priority Rules
7 - Closures
7.1 Understanding Lexical Scope
7.2 What are Closures?
7.3 How Closures Work
7.4 Practical Closure Patterns
7.4.1 Private Variables
7.4.2 Function Factories
7.4.3 Module Pattern
7.4.4 Memoization
7.4.5 Event Listeners and Callbacks
7.5 Closure Performance Considerations
7.6 Common Closure Pitfalls
8 - Higher-Order Functions
8.1 Functions as First-Class Citizens
8.2 Functions Accepting Functions (Callbacks)
8.3 Functions Returning Functions
8.4 Function Composition
8.5 Currying
8.5.1 What is Currying?
8.5.2 Implementing Currying
8.5.3 Partial Application vs Currying
8.6 Practical Higher-Order Functions
8.6.1 once()
8.6.2 debounce()
8.6.3 throttle()
8.6.4 memoize()
8.7 built-in-higher-order-functions
9 - Recursion
9.1 Understanding Recursion
9.2 Base Case and Recursive Case
9.3 The Call Stack in Recursion
9.4 Tail Call Optimization
9.5 Common Recursive Problems
9.5.1 Factorial
9.5.2 Fibonacci
9.5.3 Tree Traversal
9.5.4 Deep Object Cloning
9.6 Recursion vs Iteration
10 - Objects Deep Dive
10.1 Object Literals
10.2 Property Accessors (dot vs bracket)
10.3 Computed Properties
10.4 Method Definitions
10.5 Object Destructuring
10.6 Property Descriptors
10.6.1 value
10.6.2 writable
10.6.3 enumerable
10.6.4 configurable
10.6.5 get and set
10.7 Object Methods
10.7.1 Object.create()
10.7.2 Object.assign()
10.7.3 Object.keys(), values(), entries()
10.7.4 Object.freeze(), seal(), preventExtensions()
10.7.5 Object.hasOwn()
10.7.6 Object.defineProperty()
10.8 Property Enumeration Order
11 - Prototypal Inheritance
11.1 Understanding Prototypes
11.2 The Prototype Chain
11.3 __proto__ vs prototype
11.4 Object.getPrototypeOf() and Object.setPrototypeOf()
11.5 The instanceof Operator
11.6 constructor Property
11.7 Creating Objects with Custom Prototypes
11.8 Inheritance Patterns
11.8.1 Prototype Chain Inheritance
11.8.2 Constructor Stealing
11.8.3 Combination Inheritance
11.8.4 Parasitic Inheritance
11.8.5 Parasitic Combination Inheritance
12 - ES6 Classes
12.1 Class Declarations and Expressions
12.2 The constructor Method
12.3 Instance Properties
12.4 Static Methods and Properties
12.5 Private Fields (#)
12.6 Getters and Setters in Classes
12.7 Inheritance with extends and super
12.8 Method Overriding
12.9 Abstract Classes (Simulation)
12.10 Mixins
12.11 Classes Under the Hood (Syntactic Sugar)
13 - Built-in Objects
13.1 The Global Object
13.2 Number Object
13.3 String Object
13.4 Boolean Object
13.5 Date Object
13.6 Math Object
13.7 RegExp Object
13.8 Error Object and Error Types
13.9 JSON Object (parse, stringify)
14 - Arrays Mastery
14.1 Creating Arrays
14.2 Array Properties (length)
14.3 Array Methods Categories
14.3.1 Mutator Methods (push, pop, shift, unshift, splice, sort, reverse, fill, copyWithin)
14.3.2 Accessor Methods (concat, slice, join, indexOf, lastIndexOf, includes)
14.3.3 Iteration Methods (forEach, map, filter, reduce, reduceRight, some, every, find, findIndex, findLast, findLastIndex)
14.4 Multidimensional Arrays
14.5 Array-Like Objects
14.5.1 arguments
14.5.2 HTML Collections
14.5.3 Converting to Arrays
14.6 Sparse Arrays
14.7 Performance Considerations
15 - Advanced Array Techniques
15.1 The reduce() Method Deep Dive
15.2 Flattening Arrays (flat, flatMap)
15.3 Sorting Custom Objects
15.4 Grouping Array Elements
15.5 Array Intersection, Union, Difference
15.6 Chaining Array Methods
15.7 Immutable Array Operations
15.8 Implementing Custom Array Methods
16 - Iterators and Generators
16.1 The Iteration Protocol
16.1.1 Iterable Protocol (Symbol.iterator)
16.1.2 Iterator Protocol (next(), done, value)
16.2 Built-in Iterables
16.3 Creating Custom Iterables
16.4 Generator Functions
16.4.1 yield Keyword
16.4.2 yield* Delegation
16.4.3 Generator Methods (next, return, throw)
16.4.4 Two-Way Communication with Generators
16.5 Practical Generator Use Cases
16.5.1 Infinite Sequences
16.5.2 Lazy Evaluation
16.5.3 Controlling Asynchronous Flows
17 - Modern Collections
17.1 Map
17.1.1 Creating and Using Maps
17.1.2 Map vs Object
17.1.3 Map Methods (set, get, has, delete, clear)
17.1.4 Iterating Maps
17.2 Set
17.2.1 Creating and Using Sets
17.2.2 Set vs Array
17.2.3 Set Methods (add, has, delete, clear)
17.2.4 Iterating Sets
17.2.5 Set Operations (union, intersection, difference)
17.3 WeakMap
17.3.1 Garbage Collection and WeakMaps
17.3.2 Use Cases (private data, caching)
17.4 WeakSet
17.5 Typed Arrays (ArrayBuffer, DataView)
18 - The Event Loop
18.1 JavaScript Runtime Architecture
18.1.1 Call Stack
18.1.2 Heap
18.1.3 Web APIs / C++ APIs
18.1.4 Callback Queue (Task Queue)
18.1.5 Microtask Queue
18.1.6 Render Queue
18.2 How the Event Loop Works
18.3 Macrotasks vs Microtasks
18.4 Event Loop Phases (Node.js)
18.5 Blocking the Event Loop
18.6 Visualizing the Event Loop
19 - Callbacks
19.1 Synchronous vs Asynchronous Callbacks
19.2 The Callback Pattern
19.3 Error-First Callbacks (Node.js style)
19.4 Callback Hell (Pyramid of Doom)
19.5 Inversion of Control
19.6 Limitations of Callbacks
20 - Promises
20.1 What is a Promise?
20.2 Promise States (pending, fulfilled, rejected)
20.3 Creating Promises (Promise constructor)
20.4 Promise Methods
20.4.1 then()
20.4.2 catch()
20.4.3 finally()
20.5 Promise Chaining
20.6 Error Propagation in Chains
20.7 Promise Static Methods
20.7.1 Promise.all()
20.7.2 Promise.allSettled()
20.7.3 Promise.race()
20.7.4 Promise.any()
20.7.5 Promise.resolve()
20.7.6 Promise.reject()
20.8 Promise Composition Patterns
20.9 Promisifying Callback-Based Functions
20.10 Implementing Promise from Scratch
21 - Async/Await
21.1 async Functions
21.2 await Expression
21.3 Error Handling with try/catch
21.4 Parallel Execution (Promise.all with await)
21.5 Sequential vs Concurrent Execution
21.6 Async/Await in Loops
21.7 Top-Level Await
21.8 Async/Await with Generators
21.9 Converting Promise Chains to Async/Await
22 - Advanced Async Patterns
22.1 Async Iterators and Generators
22.2 for await...of Loop
22.3 Async Generators
22.4 Cancellation Patterns (AbortController)
22.5 Timeouts and Race Conditions
22.6 Retry Patterns
22.7 Rate Limiting and Throttling Async Operations
22.8 Batching and Caching Async Operations
22.9 Observable Pattern (Introduction)
22.10 Async Queue Implementation
23 - Web Workers (Browser)
23.1 Why Web Workers?
23.2 Dedicated Workers
23.2.1 Creating a Worker
23.2.2 Communication (postMessage, onmessage)
23.2.3 Error Handling
23.2.4 Terminating Workers
23.3 Shared Workers
23.4 Service Workers (Overview)
23.5 Transferable Objects
23.6 Worker Limitations
23.7 Performance Considerations
24 - Metaprogramming with Proxies and Reflect
24.1 What is Metaprogramming?
24.2 Proxy Fundamentals
24.2.1 Creating Proxies (target, handler)
24.2.2 Revocable Proxies
24.3 Proxy Traps
24.3.1 get and set
24.3.2 has (in operator)
24.3.3 deleteProperty
24.3.4 apply (function calls)
24.3.5 construct (new operator)
24.3.6 getPrototypeOf and setPrototypeOf
24.3.7 defineProperty
24.3.8 getOwnPropertyDescriptor
24.3.9 ownKeys
24.3.10 isExtensible and preventExtensions
24.4 Practical Proxy Use Cases
24.4.1 Validation
24.4.2 Logging and Profiling
24.4.3 Observability (Change Detection)
24.4.4 Caching
24.4.5 Default Values
24.4.6 Virtual Properties
24.4.7 Revocable References
24.5 The Reflect API
24.5.1 Reflect Methods (matching traps)
24.5.2 Using Reflect in Proxies
25 - Symbols
25.1 Creating Symbols
25.2 Symbol Characteristics (unique, not enumerable)
25.3 Global Symbol Registry (Symbol.for, Symbol.keyFor)
25.4 Well-Known Symbols
25.4.1 Symbol.iterator
25.4.2 Symbol.asyncIterator
25.4.3 Symbol.hasInstance
25.4.4 Symbol.isConcatSpreadable
25.4.5 Symbol.match, Symbol.replace, Symbol.search, Symbol.split
25.4.6 Symbol.species
25.4.7 Symbol.toPrimitive
25.4.8 Symbol.toStringTag
25.4.9 Symbol.unscopables
25.5 Use Cases for Symbols
25.5.1 Private Properties (convention)
25.5.2 Avoiding Property Name Collisions
25.5.3 Defining Custom Behavior
26 - Memory Management
26.1 Memory Life Cycle
26.2 Garbage Collection
26.2.1 Reference Counting
26.2.2 Mark-and-Sweep
26.2.3 Generational Collection
26.2.4 Incremental Collection
26.3 Memory Leaks
26.3.1 Accidental Global Variables
26.3.2 Forgotten Timers and Callbacks
26.3.3 Closures Causing Leaks
26.3.4 Detached DOM Elements
26.3.5 Event Listeners
26.3.6 Circular References
26.4 Detecting Memory Leaks
26.4.1 Chrome DevTools Memory Tab
26.4.2 Heap Snapshots
26.4.3 Allocation Timeline
26.4.4 Performance Monitor
26.5 Weak References (WeakMap, WeakSet, WeakRef)
26.6 FinalizationRegistry
27 - Modules
27.1 The Need for Modules
27.2 Module Formats History
27.2.1 IIFE Modules
27.2.2 CommonJS (require, module.exports)
27.2.3 AMD (Asynchronous Module Definition)
27.2.4 UMD (Universal Module Definition)
27.3 ES6 Modules
27.3.1 Named Exports/Imports
27.3.2 Default Exports/Imports
27.3.3 Mixed Exports
27.3.4 Renaming Imports/Exports (as)
27.3.5 Namespace Imports (* as)
27.3.6 Re-exporting (export from)
27.4 Dynamic Imports (import())
27.5 Module Resolution
27.6 Circular Dependencies
27.7 Tree Shaking
27.8 Modules in Browsers vs Node.js
27.9 Module Bundlers (Conceptual Understanding)
28 - Regular Expressions
28.1 Creating Regular Expressions
28.2 RegExp Methods (test, exec)
28.3 String Methods with RegExp (match, matchAll, search, replace, split)
28.4 Pattern Syntax
28.4.1 Character Classes
28.4.2 Quantifiers
28.4.3 Groups and Ranges
28.4.4 Assertions (Lookahead, Lookbehind)
28.4.5 Flags (g, i, m, s, u, y)
28.5 Advanced RegExp Features
28.5.1 Named Capture Groups
28.5.2 Backreferences
28.5.3 Unicode Property Escapes
28.6 Performance Considerations
28.7 Common RegExp Patterns
28.8 Debugging Regular Expressions
29 - Debugging JavaScript
29.1 Console API Mastery
29.1.1 console.log, info, warn, error
29.1.2 console.table
29.1.3 console.group, groupCollapsed, groupEnd
29.1.4 console.time, timeLog, timeEnd
29.1.5 console.count, countReset
29.1.6 console.trace
29.1.7 console.dir, dirxml
29.1.8 console.assert
29.1.9 console.clear
29.2 Chrome DevTools
29.2.1 Sources Panel
29.2.1.1 Breakpoints (line, conditional, DOM, event listener)
29.2.1.2 Stepping Through Code
29.2.1.3 Watch Expressions
29.2.1.4 Call Stack
29.2.1.5 Scope Variables
29.2.1.6 Blackboxing Scripts
29.2.2 Debugging with debugger Statement
29.2.3 Debugging Async Code
29.2.4 Debugging Memory Issues (Heap Snapshots)
29.2.5 Performance Profiling
29.2.6 Network Panel for API Debugging
29.3 VS Code Debugger
29.3.1 Launch Configurations
29.3.2 Attaching to Node.js Processes
29.3.3 Debugging Tests
29.4 Node.js Debugging
29.4.1 Inspector
29.4.2 ndb
30 - Code Quality and Linting
30.1 ESLint
30.1.1 Installation and Configuration
30.1.2 Rules (errors, warnings, off)
30.1.3 Plugins
30.1.4 Extending Configs
30.1.5 .eslintrc Formats
30.1.6 Ignoring Files
30.1.7 Fixing Automatically
30.2 Prettier
30.2.1 Opinionated Formatting
30.2.2 Integration with ESLint
30.2.3 Configuration Options
30.3 EditorConfig
30.4 Husky and lint-staged (Git Hooks)
30.5 JSDoc Comments
30.5.1 @param, @returns, @throws
30.5.2 @typedef for Custom Types
30.5.3 Generating Documentation
31 - Testing JavaScript
31.1 Testing Fundamentals
31.1.1 Why Test?
31.1.2 Types of Tests (Unit, Integration, E2E)
31.1.3 Test Pyramid
31.2 Unit Testing with Jest
31.2.1 Setup and Configuration
31.2.2 Matchers (toBe, toEqual, toContain, toThrow)
31.2.3 Setup and Teardown (beforeEach, afterAll)
31.2.4 Mocking Functions (jest.fn(), jest.spyOn())
31.2.5 Mocking Modules (jest.mock())
31.2.6 Mocking Timers (jest.useFakeTimers())
31.2.7 Testing Async Code
31.2.8 Code Coverage
31.3 Alternative Test Runners (Mocha, Jasmine, Vitest)
31.4 Assertion Libraries (Chai, expect)
31.5 Test-Driven Development (TDD) with JavaScript
31.5.1 Red-Green-Refactor Cycle
31.5.2 Writing Tests First
31.5.3 Refactoring Safely
31.6 Property-Based Testing (fast-check)
32 - JavaScript Performance
32.1 Measuring Performance
32.1.1 Performance API (performance.now())
32.1.2 console.time
32.1.3 Chrome DevTools Performance Tab
32.1.4 Lighthouse Audits
32.2 JavaScript Engine Optimizations
32.2.1 Hidden Classes
32.2.2 Inline Caching
32.2.3 Just-In-Time (JIT) Compilation
32.2.4 Garbage Collection Impact
32.3 Code-Level Optimizations
32.3.1 Loop Optimizations
32.3.2 Function Inlining
32.3.3 Memoization
32.3.4 Debouncing and Throttling
32.3.5 Lazy Evaluation
32.3.6 Avoiding Memory Leaks
32.4 DOM Interaction Performance
32.4.1 Reflow and Repaint
32.4.2 Batch DOM Updates
32.4.3 Document Fragments
32.4.4 requestAnimationFrame
32.4.5 Virtual Scrolling
32.5 Network Performance
32.5.1 Minimizing Bundle Size
32.5.2 Code Splitting
32.5.3 Lazy Loading
32.5.4 Preloading, Prefetching, Preconnecting
33 - Design Patterns in JavaScript
33.1 Creational Patterns
33.1.1 Singleton
33.1.2 Factory Method
33.1.3 Abstract Factory
33.1.4 Builder
33.1.5 Prototype
33.2 Structural Patterns
33.2.1 Adapter
33.2.2 Decorator
33.2.3 Proxy
33.2.4 Facade
33.2.5 Bridge
33.2.6 Composite
33.2.7 Flyweight
33.3 Behavioral Patterns
33.3.1 Observer
33.3.2 Strategy
33.3.3 Command
33.3.4 Iterator (already covered)
33.3.5 Mediator
33.3.6 Memento
33.3.7 State
33.3.8 Template Method
33.3.9 Visitor
33.3.10 Chain of Responsibility
33.4 JavaScript-Specific Patterns
33.4.1 Module Pattern
33.4.2 Revealing Module Pattern
33.4.3 Singleton in ES6
33.4.4 Mixins
33.4.5 Middleware Pattern
34 - Document Object Model (DOM)
34.1 DOM Tree Structure
34.2 Selecting Elements
34.2.1 getElementById
34.2.2 getElementsByClassName
34.2.3 getElementsByTagName
34.2.4 querySelector and querySelectorAll
34.3 Traversing the DOM
34.3.1 Parent, Child, Sibling Relationships
34.3.2 closest(), matches()
34.4 Manipulating Elements
34.4.1 Creating Elements (createElement)
34.4.2 Inserting Elements (appendChild, insertBefore, append, prepend)
34.4.3 Removing Elements (removeChild, remove)
34.4.4 Cloning Elements (cloneNode)
34.4.5 innerHTML vs textContent
34.5 Attributes and Properties
34.5.1 getAttribute, setAttribute, removeAttribute
34.5.2 dataset (data-* attributes)
34.5.3 Class Manipulation (classList)
34.6 Styles and CSS
34.6.1 style Property
34.6.2 getComputedStyle
34.6.3 className and classList
35 - Events
35.1 Event Types
35.1.1 Mouse Events
35.1.2 Keyboard Events
35.1.3 Form Events
35.1.4 Focus Events
35.1.5 Touch Events
35.1.6 Drag and Drop Events
35.1.7 Custom Events
35.2 Event Handlers
35.2.1 Inline Event Handlers (onclick)
35.2.2 DOM Property Handlers
35.2.3 addEventListener
35.2.4 removeEventListener
35.3 Event Object
35.3.1 Properties (type, target, currentTarget)
35.3.2 Methods (preventDefault, stopPropagation, stopImmediatePropagation)
35.4 Event Propagation
35.4.1 Capturing Phase
35.4.2 Target Phase
35.4.3 Bubbling Phase
35.5 Event Delegation
35.6 Custom Events (CustomEvent)
36 - Browser Storage
36.1 Cookies
36.1.1 Setting and Reading Cookies
36.1.2 Cookie Attributes (expires, path, domain, secure, HttpOnly, SameSite)
36.2 Web Storage API
36.2.1 localStorage
36.2.2 sessionStorage
36.2.3 Storage Events
36.3 IndexedDB
36.3.1 Opening a Database
36.3.2 Object Stores
36.3.3 Transactions
36.3.4 CRUD Operations
36.3.5 Indexes
36.3.6 Cursors
36.4 Cache API (Service Workers)
37 - Network Requests
37.1 XMLHttpRequest (Legacy)
37.2 Fetch API
37.2.1 Basic Fetch
37.2.2 Request and Response Objects
37.2.3 Headers
37.2.4 Body Methods (json, text, blob, formData)
37.2.5 Error Handling
37.2.6 Aborting Fetch (AbortController)
37.3 WebSockets
37.3.1 WebSocket API
37.3.2 Sending and Receiving Messages
37.3.3 Connection Management
37.4 Server-Sent Events (EventSource)
38 - Internationalization (i18n)
38.1 Intl Object Overview
38.2 Number Formatting (Intl.NumberFormat)
38.3 Date and Time Formatting (Intl.DateTimeFormat)
38.4 Collation (Intl.Collator)
38.5 Pluralization (Intl.PluralRules)
38.6 Relative Time (Intl.RelativeTimeFormat)
38.7 List Formatting (Intl.ListFormat)
39 - Security in JavaScript
39.1 Cross-Site Scripting (XSS)
39.1.1 Reflected XSS
39.1.2 Stored XSS
39.1.3 DOM-based XSS
39.1.4 Prevention Strategies (escaping, CSP)
39.2 Cross-Site Request Forgery (CSRF)
39.3 Content Security Policy (CSP)
39.4 Same-Origin Policy and CORS
39.5 iframe Security (sandbox)
39.6 Subresource Integrity (SRI)
39.7 Secure Cookies (HttpOnly, Secure, SameSite)
40 - JavaScript Runtimes and Environments
40.1 Browser JavaScript
40.1.1 window Object
40.1.2 document Object
40.1.3 navigator Object
40.1.4 location Object
40.1.5 history Object
40.2 Node.js JavaScript
40.2.1 global Object
40.2.2 process Object
40.2.3 Buffer
40.2.4 __dirname, __filename
40.2.5 module and require
40.3 Deno and Bun (Alternative Runtimes)
40.4 WebAssembly and JavaScript
GitHub
Select language
English
Français
Measuring Performance