JavaScript Style Guide

Relevant source files

• README.md

Purpose and Scope

This document describes the core JavaScript style guide for the Airbnb JavaScript Style Guide repository, as documented in README.md1-4098 The guide defines fundamental language patterns, syntax conventions, and best practices for writing modern JavaScript (ES6+). It assumes the use of Babel transpilation via babel-preset-airbnb and browser polyfills via airbnb-browser-shims README.md5-6

For details on specific topics, see the following child pages:

• Types, Variables, and References
• Objects, Arrays, and Destructuring
• Strings and Template Literals
• Functions and Arrow Functions
• Classes, Modules, and Iterators
• Comparison Operators and Control Flow
• Code Style and Formatting

Sources: README.md1-10

Style Guide Organization

The JavaScript style guide is organized into 30 major sections covering language fundamentals through testing and performance considerations README.md21-61 The core rules are enforced via ESLint configurations in eslint-config-airbnb and eslint-config-airbnb-base packages.

Language Architecture Overview

The following diagram maps high-level style categories to the specific code entities and rules that govern them.

Sources: README.md21-61 README.md63-3820

Core Language Fundamentals

Types and References

JavaScript distinguishes between primitive types like string, number, and boolean (pass-by-value) and complex types like object and array (pass-by-reference) README.md65-105 The guide mandates const for all references to ensure they cannot be reassigned, and let only when reassignment is necessary, strictly prohibiting var due to its function-scoping behavior README.md111-143

For details, see Types, Variables, and References.

Sources: README.md63-162

Objects, Arrays, and Destructuring

The guide enforces literal syntax for objects and arrays ({} and []), discouraging the use of constructors like new Object() README.md166-174 It promotes modern ES6+ features such as computed property names, object method shorthand, and the spread operator for creating shallow copies README.md178-224 Destructuring is required when accessing and using multiple properties of an object or array README.md468-477

For details, see Objects, Arrays, and Destructuring.

Sources: README.md164-576

Strings and Template Literals

Single quotes (') are the standard for strings README.md580-588 Template literals (backticks) are required when programmatically building strings or for multi-line strings to avoid manual concatenation README.md611-628

For details, see Strings and Template Literals.

Sources: README.md578-659

Execution and Structure

Functions and Arrow Functions

The guide prioritizes named function expressions over function declarations to prevent hoisting issues README.md663-688 Arrow functions are required for anonymous callbacks and situations requiring lexical this README.md884-904

For details, see Functions and Arrow Functions.

Sources: README.md661-1107

Classes, Modules, and Iterators

ES6 class syntax is mandatory over direct prototype manipulation README.md1111-1118 The module system relies on import/export syntax rather than non-standard module systems README.md1240-1248 Functional iteration methods like map(), every(), and reduce() are preferred over for-in or for-of loops to emphasize immutable data patterns README.md1396-1415

For details, see Classes, Modules, and Iterators.

Sources: README.md1109-1591

Logic and Formatting

Comparison and Control Flow

Strict equality (===) is required over abstract equality (==) README.md2024-2035 The guide provides specific truthiness rules for booleans and dictates the structure of blocks, including "cuddled" else statements and mandatory braces for all control statements README.md2250-2270

For details, see Comparison Operators and Control Flow.

Sources: README.md2022-2419

Code Style and Formatting

This covers the visual consistency of the codebase: 2-space indentation, 100-character line limits, mandatory semicolons, and trailing commas README.md2618-3162 It also defines naming conventions like camelCase for variables/functions and PascalCase for classes/constructors README.md3300-3340

For details, see Code Style and Formatting.

Sources: README.md2562-3575

ESLint Rule Integration

The style guide is implemented through a series of ESLint rules defined in the configuration packages.

Code Entity to ESLint Rule Mapping

The following diagram bridges natural language style requirements to the specific ESLint rules used in the codebase to enforce them.

Sources: README.md112 README.md127 README.md167 README.md2024

Standard Library and Testing

The guide extends to the usage of the JavaScript standard library and testing practices:

• Standard Library: Prefer Number.isNaN() over the global isNaN() and Number.isFinite() over global isFinite() for more reliable type checking README.md3781-3819
• Testing: Recommends small, pure functions to facilitate testing with frameworks like Jest or Mocha, and suggests maintaining high test coverage README.md3821-3841

Sources: README.md3781-3841