eslint/docs/user-guide/getting-started.md

   1 # Getting Started with ESLint
   2
   3 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:
   4
   5 * ESLint uses [Espree](https://github.com/eslint/espree) for JavaScript parsing.
   6 * ESLint uses an AST to evaluate patterns in code.
   7 * ESLint is completely pluggable, every single rule is a plugin and you can add more at runtime.
   8
   9 ## Installation and Usage
  10
  11 Prerequisites: [Node.js](https://nodejs.org/en/) (`^12.22.0`, `^14.17.0`, or `>=16.0.0`) built with SSL support. (If you are using an official Node.js distribution, SSL is always built in.)
  12
  13 You can install ESLint using npm or yarn:
  14
  15 ```sh
  16 npm install eslint --save-dev
  17
  18 # or
  19
  20 yarn add eslint --dev
  21 ```
  22
  23 You should then set up a configuration file, and the easiest way to do that is to use the `--init` flag:
  24
  25 ```sh
  26 $ npx eslint --init
  27
  28 # or
  29
  30 $ yarn run eslint --init
  31 ```
  32
  33 **Note:** `--init` assumes you have a `package.json` file already. If you don't, make sure to run `npm init` or `yarn init` beforehand.
  34
  35 After that, you can run ESLint on any file or directory like this:
  36
  37 ```sh
  38 $ npx eslint yourfile.js
  39
  40 # or
  41
  42 $ yarn run eslint yourfile.js
  43 ```
  44
  45 It is also possible to install ESLint globally rather than locally (using `npm install eslint --global`). However, this is not recommended, and any plugins or shareable configs that you use must be installed locally in either case.
  46
  47 ## Configuration
  48
  49 **Note:** If you are coming from a version before 1.0.0 please see the [migration guide](migrating-to-1.0.0.md).
  50
  51 After running `eslint --init`, you'll have a `.eslintrc.{js,yml,json}` file in your directory. In it, you'll see some rules configured like this:
  52
  53 ```json
  54 {
  55     "rules": {
  56         "semi": ["error", "always"],
  57         "quotes": ["error", "double"]
  58     }
  59 }
  60 ```
  61
  62 The names `"semi"` and `"quotes"` are the names of [rules](/docs/rules) in ESLint. The first value is the error level of the rule and can be one of these values:
  63
  64 * `"off"` or `0` - turn the rule off
  65 * `"warn"` or `1` - turn the rule on as a warning (doesn't affect exit code)
  66 * `"error"` or `2` - turn the rule on as an error (exit code will be 1)
  67
  68 The three error levels allow you fine-grained control over how ESLint applies rules (for more configuration options and details, see the [configuration docs](configuring/)).
  69
  70 Your `.eslintrc.{js,yml,json}` configuration file will also include the line:
  71
  72 ```json
  73 {
  74     "extends": "eslint:recommended"
  75 }
  76 ```
  77
  78 Because of this line, all of the rules marked "(recommended)" on the [rules page](/docs/rules) will be turned on.  Alternatively, you can use configurations that others have created by searching for "eslint-config" on [npmjs.com](https://www.npmjs.com/search?q=eslint-config).  ESLint will not lint your code unless you extend from a shared configuration or explicitly turn rules on in your configuration.
  79
  80 ---
  81
  82 ## Next Steps
  83
  84 * Learn about [advanced configuration](configuring/) of ESLint.
  85 * Get familiar with the [command line options](command-line-interface.md).
  86 * Explore [ESLint integrations](integrations.md) into other tools like editors, build systems, and more.
  87 * Can't find just the right rule?  Make your own [custom rule](/docs/developer-guide/working-with-rules.md).
  88 * Make ESLint even better by [contributing](/docs/developer-guide/contributing/).