Biome Lint & TypeScript Type-Check

Quick Reference

Error	Fix
`noImplicitAnyLet`	Add type: `let x;` → `let x: Type;`
`noUnusedVariables`	Prefix `_`: `const foo` → `const _foo`
`noUnusedFunctionParameters`	Rename in destructure: `{ param }` → `{ param: _param }`
`noEmptyPattern`	Replace `{}` with `_opts: object`
`noUnreachable`	Remove dead code or wrap in block comment
`noInvalidUseBeforeDeclaration`	Move declaration before usage or extract to const
`TS2322`	Type assertion or filter: `as Record<string, string>`
`TS2345`	Non-null assertion or default: `value!` or `value ?? ''`
`TS7030`	Add explicit return: `return undefined;`
`TS2339`	Type assertion to extend: `as Type & { prop?: T }`

Workflow

Biome Lint

# 1. Auto-fix
pnpm biome lint ./src --write

# 2. Check remaining errors
pnpm biome lint ./src

# 3. Fix import type issues
npx -y @biomejs/biome lint --only=style/useImportType ./src --write

TypeScript Check

# Single package
pnpm tsgo -p tsconfig.json --skipLibCheck --maxNodeModuleJsDepth 0 --noEmit

# All packages
pnpm -r exec just typecheck

Per-Package Rule Override

Create local biome.json to override rules:

{
  "root": false,
  "extends": "//",
  "linter": {
    "rules": {
      "correctness": { "useHookAtTopLevel": "warn" },
      "a11y": { "useButtonType": "warn" }
    }
  }
}

biome-ignore Comments

// biome-ignore lint/suspicious/noSelfCompare: NaN check
return x !== x;

// biome-ignore lint/correctness/noConstructorReturn: proxy pattern
return new Proxy();

Detailed Guides

Biome fixes — Full fix examples for each Biome rule
TypeScript fixes — TS errors, ES version issues, cross-package deps
Breaking changes — Zod 4, vitest 4, react-router v7, etc.

biome-lint

Biome Lint & TypeScript Type-Check

Quick Reference

Workflow

Biome Lint

TypeScript Check

Per-Package Rule Override

biome-ignore Comments

Detailed Guides