ESLint Setup for JavaScript/TypeScript Linting

ESLint Configuration for JavaScript/TypeScript Linting

ESLint is a static code analyzer. It catches errors before running, ensures style consistency, prevents anti-patterns. Since version 9 moved to flat config — new configuration format that's easier to read and faster to parse.

Installation

npm install --save-dev eslint @eslint/js typescript-eslint

For React projects additionally:

npm install --save-dev eslint-plugin-react eslint-plugin-react-hooks eslint-plugin-jsx-a11y

eslint.config.mjs (flat config, ESLint 9+)

import js from '@eslint/js';
import tseslint from 'typescript-eslint';
import reactPlugin from 'eslint-plugin-react';
import reactHooks from 'eslint-plugin-react-hooks';
import jsxA11y from 'eslint-plugin-jsx-a11y';

export default tseslint.config(
  // Base JS rules
  js.configs.recommended,

  // TypeScript
  ...tseslint.configs.recommendedTypeChecked,
  {
    languageOptions: {
      parserOptions: {
        project: './tsconfig.json',
        tsconfigRootDir: import.meta.dirname,
      },
    },
  },

  // React
  {
    plugins: {
      react: reactPlugin,
      'react-hooks': reactHooks,
      'jsx-a11y': jsxA11y,
    },
    settings: {
      react: { version: 'detect' },
    },
    rules: {
      ...reactPlugin.configs.recommended.rules,
      ...reactHooks.configs.recommended.rules,
      ...jsxA11y.configs.recommended.rules,
      'react/react-in-jsx-scope': 'off',  // React 17+ JSX transform
      'react/prop-types': 'off',          // using TypeScript
    },
  },

  // Custom rules
  {
    rules: {
      // TypeScript
      '@typescript-eslint/no-explicit-any': 'warn',
      '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
      '@typescript-eslint/consistent-type-imports': ['error', { prefer: 'type-imports' }],
      '@typescript-eslint/no-floating-promises': 'error',
      '@typescript-eslint/await-thenable': 'error',

      // Common
      'no-console': ['warn', { allow: ['warn', 'error'] }],
      'prefer-const': 'error',
      'no-var': 'error',
    },
  },

  // Ignored files
  {
    ignores: ['dist/**', 'node_modules/**', '*.config.js', 'coverage/**'],
  }
);

Scripts in package.json

{
  "scripts": {
    "lint": "eslint src",
    "lint:fix": "eslint src --fix",
    "lint:ci": "eslint src --max-warnings 0"
  }
}

--max-warnings 0 in CI — warnings treated as errors, pipeline fails.

Timeline

Basic ESLint setup for React/TypeScript project: 1–2 hours. Full setup with TypeScript type checking, custom rules, pre-commit hooks: 4–6 hours.