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/) (`^10.12.0`, or `>=12.0.0`) 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 ```
  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:
  24
  25 ```
  26 $ npx eslint --init
  27 ```
  28
  29 After that, you can run ESLint on any file or directory like this:
  30
  31 ```
  32 $ npx eslint yourfile.js
  33 ```
  34
  35 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.
  36
  37 ## Configuration
  38
  39 **Note:** If you are coming from a version before 1.0.0 please see the [migration guide](migrating-to-1.0.0.md).
  40
  41 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:
  42
  43 ```json
  44 {
  45     "rules": {
  46         "semi": ["error", "always"],
  47         "quotes": ["error", "double"]
  48     }
  49 }
  50 ```
  51
  52 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:
  53
  54 * `"off"` or `0` - turn the rule off
  55 * `"warn"` or `1` - turn the rule on as a warning (doesn't affect exit code)
  56 * `"error"` or `2` - turn the rule on as an error (exit code will be 1)
  57
  58 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.md)).
  59
  60 Your `.eslintrc.{js,yml,json}` configuration file will also include the line:
  61
  62 ```json
  63 {
  64     "extends": "eslint:recommended"
  65 }
  66 ```
  67
  68 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.
  69
  70 ---
  71
  72 ## Next Steps
  73
  74 * Learn about [advanced configuration](configuring.md) of ESLint.
  75 * Get familiar with the [command line options](command-line-interface.md).
  76 * Explore [ESLint integrations](integrations.md) into other tools like editors, build systems, and more.
  77 * Can't find just the right rule?  Make your own [custom rule](/docs/developer-guide/working-with-rules.md).
  78 * Make ESLint even better by [contributing](/docs/developer-guide/contributing/).