eslint

ESLint

Quick Start

Prerequisites

• Node.js (^18.18.0, ^20.9.0, or >=21.1.0) with SSL support
• Existing package.json file (run npm init if needed)

Installation & Setup

Automated Setup (Recommended):

npm init @eslint/config@latest

This interactive setup will ask about your project and create an eslint.config.js file.

Manual Setup:

# Install ESLint packages
npm install --save-dev eslint@latest @eslint/js@latest

# Create configuration file
touch eslint.config.js

Basic Configuration

The new flat config format (ESLint 9.0+) uses eslint.config.js:

import { defineConfig } from "eslint/config";
import js from "@eslint/js";

export default defineConfig([
  {
    files: ["**/*.js"],
    plugins: { js },
    extends: ["js/recommended"],
    rules: {
      "no-unused-vars": "warn",
      "no-undef": "warn"
    }
  }
]);

Running ESLint

# Lint a single file
npx eslint yourfile.js

# Lint a directory
npx eslint src/

# Lint with auto-fix
npx eslint src/ --fix

Core ESLint Tasks

1. Setting Up ESLint

For JavaScript Projects

npm init @eslint/config@latest

Select options:

• How would you like to use ESLint? → To check syntax, find problems, and enforce code style
• What type of modules? → JavaScript modules (import/export)
• Which framework? → None/React/Vue (as applicable)
• Does your project use TypeScript? → No
• Where does your code run? → Browser and/or Node
• Config file format → JavaScript/JSON/YAML (JavaScript recommended)

For TypeScript Projects

npm install --save-dev eslint@latest @typescript-eslint/parser @typescript-eslint/eslint-plugin typescript-eslint

Configuration for TypeScript:

import { defineConfig } from 'eslint/config';
import eslint from '@eslint/js';
import tseslint from 'typescript-eslint';

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