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Quick Start Guide

Get ESLint analyzing your JavaScript code in under 5 minutes. This guide will walk you through the essentials.

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Prerequisites

Before you begin, ensure you have Node.js installed:
Required: Node.js ^20.19.0, ^22.13.0, or >=24 built with SSL support.Check your version: node --version

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Installation & Setup

1

Initialize ESLint Configuration

Run the interactive configuration wizard to set up ESLint for your project:
npm init @eslint/config@latest
This command will:
  • Detect your project type (JavaScript, TypeScript, React, etc.)
  • Ask about your code style preferences
  • Install required dependencies
  • Create an eslint.config.js file
The wizard is smart enough to detect if you’re using React, Vue, or TypeScript and will configure ESLint accordingly.
2

Run Your First Lint

Lint a single file:
npx eslint yourfile.js
Or lint an entire directory:
npx eslint src/

$ npx eslint src/index.js
# No output means no problems found!
3

Fix Problems Automatically

Many ESLint errors can be fixed automatically. Run with the --fix flag:
npx eslint --fix yourfile.js
This will automatically fix:
  • Spacing and indentation issues
  • Missing semicolons
  • Quote style inconsistencies
  • And many other stylistic problems
The --fix flag modifies your files in place. Make sure your code is committed or backed up before running it.
4

Add Lint Script to package.json

Add ESLint to your npm scripts for easy access:
package.json
{
  "scripts": {
    "lint": "eslint .",
    "lint:fix": "eslint --fix ."
  }
}
Now you can run:
npm run lint      # Check for problems
npm run lint:fix  # Fix problems automatically

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Understanding the Config File

The configuration wizard creates an eslint.config.js file. Here’s what a basic config looks like:
eslint.config.js
import { defineConfig } from "eslint/config";

export default defineConfig([
  {
    files: ["**/*.js", "**/*.cjs", "**/*.mjs"],
    rules: {
      "prefer-const": "warn",
      "no-constant-binary-expression": "error",
    },
  },
]);

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Configuration Breakdown

Specifies which files ESLint should analyze. Supports glob patterns:
files: ["**/*.js", "**/*.cjs", "**/*.mjs"]
This matches all .js, .cjs, and .mjs files in any directory.
Configures individual rules with severity levels:
  • "off" or 0 - Disable the rule
  • "warn" or 1 - Show warning (exit code 0)
  • "error" or 2 - Show error (exit code 1)
rules: {
  "no-unused-vars": "error",
  "no-console": "warn",
  "quotes": ["error", "double"],
}
Import configurations from presets:
import js from "@eslint/js";

export default defineConfig([
  js.configs.recommended,  // Use recommended rules
  {
    // Your custom rules
  },
]);

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Common Rules to Start With

Here are some essential rules from the ESLint source code:

no-unused-vars

Type: Problem
Recommended: ✓Disallow unused variables to keep your code clean.
// ❌ Error
const x = 5; // 'x' is never used

// ✓ Correct
const x = 5;
console.log(x);

no-undef

Type: Problem
Recommended: ✓Disallow undefined variables to catch typos early.
// ❌ Error
console.log(foo); // 'foo' is not defined

// ✓ Correct
const foo = 'bar';
console.log(foo);

prefer-const

Type: Suggestion
Fixable: ✓Suggest using const for variables that are never reassigned.
// ⚠ Warning
let x = 5; // 'x' is never reassigned

// ✓ Correct
const x = 5;

no-debugger

Type: Problem
Recommended: ✓Disallow debugger statements in production code.
// ❌ Error
debugger;

// ✓ Use proper debugging tools instead

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CLI Options Quick Reference

Here are the most commonly used CLI options from ESLint’s source: 
# Fix problems automatically
eslint --fix file.js

# Use a specific config file
eslint -c custom-config.js file.js

# Specify output format
eslint --format json file.js

# Set maximum warnings before error
eslint --max-warnings 10 .

# Lint with quiet mode (errors only)
eslint --quiet file.js

# Debug mode for troubleshooting
eslint --debug file.js
For a complete list of CLI options, run npx eslint --help or check the options.js source file.

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What’s Next?

Deep Dive into Installation

Learn about advanced installation options, pnpm setup, and TypeScript configuration

Configuration Guide

Master ESLint’s powerful configuration system

Rules Reference

Browse all 200+ built-in rules with examples

Create Custom Rules

Build your own rules to enforce project-specific patterns

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Troubleshooting

Make sure your config file is named eslint.config.js, eslint.config.mjs, or eslint.config.cjs and is in your project root.You can also specify a config file explicitly:
npx eslint -c path/to/config.js file.js
This usually means ESLint can’t parse your JavaScript syntax. If you’re using modern syntax or TypeScript:
npm install --save-dev @typescript-eslint/parser
Then update your config:
import tsParser from "@typescript-eslint/parser";

export default defineConfig([
  {
    languageOptions: {
      parser: tsParser,
    },
  },
]);
Check that:
  1. The files pattern matches your source files
  2. The rule is spelled correctly (e.g., no-unused-vars, not no-unused-variables)
  3. Your config file is being loaded (run with --debug flag)
npx eslint --debug file.js

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