ESLint

ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code. In many ways, it is similar to JSLint and JSHint with a few exceptions:

ESLint uses Espree for JavaScript parsing.
ESLint uses an AST to evaluate patterns in code.
ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.

Configuration

After running npm init @eslint/config, you’ll have an eslint.config.js (or eslint.config.mjs) file in your directory. In it, you’ll see some rules configured like this:

import pluginJs from "@eslint/js";
export default [ pluginJs.configs.recommended, ];

The names "semi" and "quotes" are the names of rules in ESLint. The first value is the error level of the rule and can be one of these values:

"off" or 0 - turn the rule off
"warn" or 1 - turn the rule on as a warning (doesn’t affect exit code)
"error" or 2 - turn the rule on as an error (exit code will be 1)

The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the configuration docs).

Code of Conduct

ESLint adheres to the JS Foundation Code of Conduct.

Filing Issues

Before filing an issue, please be sure to read the guidelines for what you’re reporting:

Frequently Asked Questions

Does Prettier replace ESLint?

No, ESLint and Prettier have different jobs: ESLint is a linter (looking for problematic patterns) and Prettier is a code formatter. Using both tools is common, refer to Prettier’s documentation to learn how to configure them to work well with each other.

Why can’t ESLint find my plugins?

Make sure your plugins (and ESLint) are both in your project’s package.json as devDependencies (or dependencies, if your project uses ESLint at runtime).
Make sure you have run npm install and all your dependencies are installed.
Make sure your plugins’ peerDependencies have been installed as well. You can use npm view eslint-plugin-myplugin peerDependencies to see what peer dependencies eslint-plugin-myplugin has.

Where to ask for help?

Open a discussion or stop by our Discord server.

Why doesn’t ESLint lock dependency versions?

Lock files like package-lock.json are helpful for deployed applications. They ensure that dependencies are consistent between environments and across deployments.

Packages like eslint that get published to the npm registry do not include lock files. npm install eslint as a user will respect version constraints in ESLint’s package.json. ESLint and its dependencies will be included in the user’s lock file if one exists, but ESLint’s own lock file would not be used.

We intentionally don’t lock dependency versions so that we have the latest compatible dependency versions in development and CI that our users get when installing ESLint in a project.

The Twilio blog has a deeper dive to learn more.

Releases

We have scheduled releases every two weeks on Friday or Saturday. You can follow a release issue for updates about the scheduling of any particular release.

Security Policy

ESLint takes security seriously. We work hard to ensure that ESLint is safe for everyone and that security issues are addressed quickly and responsibly. Read the full security policy.