Google TypeScript Style Guide Reference

Google TypeScript Style Guide に基づくコーディングリファレンスです。TypeScriptの実装・コードレビュー・リファクタリング・ESLint設定時に、Googleのコーディング規約に準拠するために使います。

How to use this reference

This guide is organized into topic-specific reference files. Read the relevant file based on the current task:

Topic	File	When to read
File structure & imports/exports	references/source-file-structure.md	Organizing files, import/export patterns, module structure
Language features	references/language-features.md	Variables, arrays, objects, classes, functions, control flow, decorators
Naming conventions	references/naming.md	Naming variables, classes, constants, type parameters, files
Type system	references/type-system.md	Type inference, null/undefined, any/unknown, interfaces vs types, generics
Comments & toolchain	references/comments-and-toolchain.md	JSDoc, comments, @ts-ignore rules, conformance

Quick Reference: Most Common Rules

These are the rules that come up most frequently. For details, read the corresponding reference file.

Naming (see references/naming.md)

• Classes/Interfaces/Types/Enums: UpperCamelCase
• Variables/functions/methods/properties: lowerCamelCase
• Global constants & enum values: CONSTANT_CASE
• Treat acronyms as words: loadHttpUrl, not loadHTTPURL
• No IMyInterface prefix for interfaces
• No trailing/leading underscores for private members

Imports & Exports (see references/source-file-structure.md)

• Use ES6 module syntax only (import/export), never require
• Use named exports exclusively; avoid default exports
• Use import type for type-only imports
• Do not use namespace; use modules
• No mutable exports (export let is prohibited)

Variables & Types (see references/language-features.md, references/type-system.md)

• Use const by default, let when reassignment needed; never var
• Use unknown over any; avoid any wherever possible
• Prefer interface over type literal aliases
• Simple arrays: T[]; complex element types: Array<{...}>
• Prefer optional (field?) over | undefined

Functions & Classes (see references/language-features.md)

• Prefer function declarations for named functions
• Use arrow functions for callbacks, not function expressions
• Mark never-reassigned properties as readonly
• Use parameter properties in constructors
• No #private fields; use TypeScript's private keyword

Control Flow (see references/language-features.md)

• Always use ===/!== (exception: == null for null/undefined check)
• Always use braces for control statements
• Only throw Error instances
• All switch must have default case
• Explicitly end statements with semicolons (no ASI reliance)

ESLint/Linter Configuration Guide

When configuring ESLint or other linters for Google TypeScript style compliance, enforce these core rules:

Must enable:

• @typescript-eslint/no-explicit-any - Discourage any usage
• @typescript-eslint/explicit-module-boundary-types - Encourage explicit return types at module boundaries
• @typescript-eslint/no-non-null-assertion - Discourage ! assertions
• eqeqeq with smart option - Enforce ===/!== with == null exception
• no-var - Forbid var
• prefer-const - Prefer const over let when no reassignment
• curly - Require braces for all control statements
• @typescript-eslint/no-namespace - Forbid namespace
• no-eval - Forbid eval()
• no-debugger - Forbid debugger
• @typescript-eslint/no-wrapper-object-types - Forbid String, Boolean, Number wrapper types
• @typescript-eslint/consistent-type-imports - Enforce import type for type-only imports
• no-restricted-syntax for WithStatement - Forbid with

Naming convention rules (@typescript-eslint/naming-convention):

• UpperCamelCase for classes, interfaces, type aliases, enums, decorators
• lowerCamelCase for variables, functions, methods, parameters, properties
• CONSTANT_CASE for global constants and enum members
• No leading/trailing underscores

Import/export rules:

• no-restricted-exports or plugin rules to forbid default exports
• @typescript-eslint/no-require-imports - Forbid require()

Additional recommended:

• @typescript-eslint/prefer-for-of - Prefer for...of
• @typescript-eslint/no-unnecessary-type-assertion - Remove unnecessary assertions
• @typescript-eslint/prefer-optional-chain - Prefer optional chaining
• @typescript-eslint/prefer-readonly - Prefer readonly for never-reassigned members