ESLint

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Find and fix problems in your JavaScript code

Find Problems

ESLint statically analyzes your code to quickly find problems. ESLint is built into most text editors and you can run ESLint as part of your continuous integration pipeline.

Fix Automatically

Many problems ESLint finds can be automatically fixed. ESLint fixes are syntax-aware so you won’t experience errors introduced by traditional find-and-replace algorithms.

Customize

Preprocess code, use custom parsers, and write your own rules that work alongside ESLint’s built-in rules. You can customize ESLint to work exactly the way you need it for your project.

Getting Started with ESLint

ESLint is a tool for identifying and reporting on patterns found in ECMAScript/JavaScript code, with the goal of making code more consistent and avoiding bugs. 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.

Configuring ESLint

ESLint is designed to be flexible and configurable for your use case. You can turn off every rule and run only with basic syntax validation or mix and match the bundled rules and your custom rules to fit the needs of your project. There are two primary ways to configure ESLint:

  1. Configuration Comments – use JavaScript comments to embed configuration information directly into a file.
  2. Configuration Files – use a JavaScript, JSON, or YAML file to specify configuration information for an entire directory and all of its subdirectories. This can be in the form of an .eslintrc.* file or an eslintConfig field in a package.json file, both of which ESLint will look for and read automatically, or you can specify a configuration file on the command line.

Here are some of the options that you can configure in ESLint:

  • Environments – which environments your script is designed to run in. Each environment brings with it a certain set of predefined global variables.
  • Globals – the additional global variables your script accesses during execution.
  • Rules – which rules are enabled and at what error level.
  • Plugins – which third-party plugins define additional rules, environments, configs, etc. for ESLint to use.

All of these options give you fine-grained control over how ESLint treats your code.

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