typescript-eslint - Quick Reference

When to Use This Skill

• Configure ESLint for TypeScript projects

• Type-aware rules for TypeScript

• Migration from TSLint

When NOT to Use This Skill

• Full ESLint 9 setup - Use eslint-biome skill for complete configuration

• Biome linter - Use eslint-biome skill for Biome setup

• Code quality principles - Use quality-common for SOLID/Clean Code

• Java/Kotlin - Use sonarqube skill for JVM languages

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: typescript-eslint for comprehensive documentation.

Basic Setup

npm install -D eslint typescript-eslint

Flat Config (ESLint 9+)

eslint.config.mjs

import eslint from '@eslint/js'; import tseslint from 'typescript-eslint';

export default tseslint.config( eslint.configs.recommended, ...tseslint.configs.recommended, );

Type-Aware Linting

import eslint from '@eslint/js'; import tseslint from 'typescript-eslint';

export default tseslint.config( eslint.configs.recommended, ...tseslint.configs.recommendedTypeChecked, { languageOptions: { parserOptions: { projectService: true, tsconfigRootDir: import.meta.dirname, }, }, }, );

Strict Configuration

export default tseslint.config( eslint.configs.recommended, ...tseslint.configs.strictTypeChecked, ...tseslint.configs.stylisticTypeChecked, );

Common Rules

{ rules: { // Prevent unused variables '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],

// Require explicit return types
'@typescript-eslint/explicit-function-return-type': 'warn',

// Prevent any usage
'@typescript-eslint/no-explicit-any': 'error',

// Require await in async functions
'@typescript-eslint/require-await': 'error',

// Prevent floating promises
'@typescript-eslint/no-floating-promises': 'error',

// Consistent type imports
'@typescript-eslint/consistent-type-imports': 'error',

} }

File-Specific Rules

export default tseslint.config( // ... base config { files: ['/*.test.ts', '/.spec.ts'], rules: { '@typescript-eslint/no-explicit-any': 'off', }, }, { files: ['**/.js'], ...tseslint.configs.disableTypeChecked, }, );

Anti-Patterns

Anti-Pattern Why It's Bad Correct Approach

Not using type-aware rules Misses Promise, async issues Use recommendedTypeChecked

Allowing any everywhere Defeats TypeScript purpose Set no-explicit-any: error

No require-await rule Unnecessary async keywords Enable type-aware async rules

Type checking JS files JS has no types Use disableTypeChecked for .js

Disabling rules in test files Tests need quality too Only disable no-explicit-any if needed

Ignoring unused variables Code smell, unused imports Use no-unused-vars with ignore pattern

Quick Troubleshooting

Issue Likely Cause Solution

Type-aware rules not working Missing projectService: true

Add to languageOptions.parserOptions

Linting very slow Type checking all files Limit type rules to **/*.ts only

"Unsafe" errors everywhere Strict type checking Use strictTypeChecked or disable specific rules

Promise errors not caught Missing no-floating-promises

Enable in recommendedTypeChecked preset

Unused imports not detected Wrong rule configuration Use @typescript-eslint/no-unused-vars

Rules conflict with Prettier Both formatting code Add eslint-config-prettier last