typescript-biome

# Biome Formatting & Linting Use **Biome** for formatting and linting in all TypeScript projects. Do not use ESLint + Prettier. ## Setup ### Dependencies ```bash npm install -D @biomejs/biome ``` ### Configuration (`biome.json`) ```json { "$schema": "https://biomejs.dev/schemas/2.0.0/schema.json", "formatter": { "indentStyle": "space", "indentWidth": 2, "lineWidth": 120 }, "javascript": { "formatter": { "quoteStyle": "single", "semicolons": "asNeeded", "arrowParentheses": "always" } }, "linter": { "rules": { "complexity": { "noBannedTypes": "error", "noUselessThisAlias": "error", "noUselessTypeConstraint": "error" }, "correctness": { "noPrecisionLoss": "error", "noUnusedVariables": "off" }, "style": { "noNamespace": "error", "useAsConstAssertion": "error", "useConsistentArrayType": { "level": "warn", "options": { "syntax": "shorthand" } } }, "suspicious": { "noDoubleEquals": "error", "noExtraNonNullAssertion": "error", "noMisleadingInstantiator": "error", "noUnsafeDeclarationMerging": "error" } } }, "assist": { "actions": { "source": { "organizeImports": { "level": "on", "options": { "groups": [ [":NODE:", "react"], [":PACKAGE:", ":PACKAGE_WITH_PROTOCOL:"], ["~/**"] ] } } } } } } ``` ## Code Style Rules ### Formatting | Setting | Value | Rationale | | --------------- | ------------- | ------------------------------------ | | Indent | 2 spaces | Standard for TypeScript/JavaScript | | Line width | 120 chars | Balances readability and screen usage | | Quotes | Single `'` | Cleaner, less visual noise | | Semicolons | As needed (ASI) | Minimal punctuation | | Arrow parens | Always | Consistent, easier to add params | | Trailing commas | All | Cleaner diffs | ### Import Organization Imports must be grouped in this order, separated by blank lines: ```ts // 1. Node builtins and React import { readFile } from 'node:fs/promises' import { join } from 'node:path' // 2. External packages import pino from 'pino' import { Injectable } from '@nestjs/common' // 3. Internal/local imports import { UserService } from '~/user/user.service' import { Config } from '~/config' ``` ### Strict Equality Always use `===` and `!==`. Never use `==` or `!=`. ```ts // Good if (value === null) {} if (typeof x === 'string') {} // Bad — will error if (value == null) {} ``` ### Array Types Use shorthand array syntax: ```ts // Good const items: string[] = [] const matrix: number[][] = [] // Bad const items: Array<string> = [] ``` Exception: use `Array<>` for complex union types: ```ts const items: Array<string | number> = [] ``` ### No Namespaces Never use TypeScript `namespace`. Use ES modules instead. ```ts // Bad namespace Utils { export function parse() {} } // Good export function parse() {} ``` ### Const Assertions Use `as const` for literal types: ```ts // Good const ROLES = ['admin', 'user', 'viewer'] as const // Bad const ROLES = ['admin', 'user', 'viewer'] ``` ## Package.json Scripts ```json { "scripts": { "format": "biome format --write .", "format:check": "biome format .", "lint": "biome lint .", "lint:fix": "biome lint --write .", "check": "biome check --write ." } } ``` ## Editor Integration Add `.vscode/settings.json` for VS Code: ```json { "editor.defaultFormatter": "biomejs.biome", "editor.formatOnSave": true, "editor.codeActionsOnSave": { "source.organizeImports.biome": "explicit" } } ``` ## Ignoring Files In `biome.json`: ```json { "files": { "ignore": ["dist", "node_modules", "*.gen.ts", "coverage"] } } ``` ## Migrating from ESLint + Prettier ```bash npx @biomejs/biome migrate eslint npx @biomejs/biome migrate prettier ``` Then remove ESLint and Prettier configs and dependencies.