eslint

What is eslint?

ESLint is a static code analysis tool for identifying problematic patterns found in JavaScript code. It is primarily used for finding and fixing problems in JavaScript code, enforcing coding standards, and improving code quality.

What are eslint's main functionalities?

Linting JavaScript Files

Run ESLint on all JavaScript files in the 'src' directory and its subdirectories.

eslint 'src/**/*.js'

Fixing Problems Automatically

Automatically fix problems in JavaScript files that ESLint is capable of fixing.

eslint --fix 'src/**/*.js'

Customizable Configuration

Customize ESLint rules and extend from recommended presets in the ESLint configuration file.

{ 'extends': 'eslint:recommended', 'rules': { 'eqeqeq': 'warn', 'no-unused-vars': 'error' } }

Integrating with Build Tools

Integrate ESLint with build tools like Grunt by using the corresponding plugin.

grunt.loadNpmTasks('grunt-eslint');

Using Plugins

Extend ESLint's capabilities with plugins for specific libraries or frameworks, such as React.

{ 'plugins': ['react'], 'rules': { 'react/jsx-uses-vars': 'error' } }

Other packages similar to eslint

jshint

JSHint is a community-driven tool that detects errors and potential problems in JavaScript code. It is less configurable than ESLint and does not support custom rule creation.

jscs

JSCS is a code style linter for programmatically enforcing your style guide. It has been deprecated and merged with ESLint, which now covers its functionality.

prettier

Prettier is an opinionated code formatter that supports many languages and integrates with most editors. Unlike ESLint, it does not check for code errors but focuses on maintaining a consistent code style.

tslint

TSLint was a linter for TypeScript, providing similar functionality to ESLint but specifically for TypeScript code. It has been deprecated in favor of typescript-eslint, which allows ESLint to be used with TypeScript.

standard

Standard is a JavaScript style guide, linter, and formatter with a set of predefined rules. It enforces a strict coding standard but is less configurable than ESLint.

README

ESLint

Website | Configuring | Rules | Contributing | Twitter | Mailing List

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.

Installation

You can install ESLint using npm:

npm install -g eslint

Usage

eslint test.js test2.js

Frequently Asked Questions

Why don't you like JSHint???

I do like JSHint. And I like Anton and Rick. Neither of those were deciding factors in creating this tool. The fact is that I've had a dire need for a JavaScript tool with pluggable linting rules. I had hoped JSHint would be able to do this, however after chatting with Anton, I found that the planned plugin infrastructure wasn't going to suit my purpose.

I'm not giving up JSHint for this!

That's not really a question, but I got it. I'm not trying to convince you that ESLint is better than JSHint. The only thing I know is that ESLint is better than JSHint for what I'm doing. In the off chance you're doing something similar, it might be better for you. Otherwise, keep using JSHint, I'm certainly not going to tell you to stop using it.

How does ESLint performance compare to JSHint?

ESLint is slower than JSHint, usually 2-3x slower on a single file. This is because ESLint uses Espree to construct an AST before it can evaluate your code whereas JSHint evaluates your code as it's being parsed. The speed is also based on the number of rules you enable; the more rules you enable, the slower the process.

Despite being slower, we believe that ESLint is fast enough to replace JSHint without causing significant pain.

Is ESLint just linting or does it also check style?

ESLint does both traditional linting (looking for problematic patterns) and style checking (enforcement of conventions). You can use it for both.

Who is using ESLint?

The following projects are using ESLint to validate their JavaScript:

• Drupal
• Esprima
• WebKit

In addition, the following companies are using ESLint internally to validate their JavaScript:

• Box
• CustomInk
• Fitbit
• HolidayCheck
• the native web

What about ECMAScript 6 support?

We are implementing ECMAScript 6 support piece-by-piece starting with version 0.12.0. You'll be able to opt-in to any ECMAScript 6 feature you want to use.

Where to ask for help?

Join our Mailing List