# eslint-loader [](https://travis-ci.org/webpack-contrib/eslint-loader)
> eslint loader for webpack
## Install
```console
$ npm install eslint-loader --save-dev
```
**NOTE**: You also need to install `eslint` from npm, if you haven't already:
```console
$ npm install eslint --save-dev
```
## Usage
In your webpack configuration
```js
module.exports = {
// ...
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
// eslint options (if necessary)
}
}
]
}
// ...
};
```
When using with transpiling loaders (like `babel-loader`), make sure they are in correct order
(bottom to top). Otherwise files will be checked after being processed by `babel-loader`
```js
module.exports = {
// ...
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
use: ["babel-loader", "eslint-loader"]
}
]
}
// ...
};
```
To be safe, you can use `enforce: "pre"` section to check source files, not modified
by other loaders (like `babel-loader`)
```js
module.exports = {
// ...
module: {
rules: [
{
enforce: "pre",
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader"
},
{
test: /\.js$/,
exclude: /node_modules/,
loader: "babel-loader"
}
]
}
// ...
};
```
### Options
You can pass [eslint options](http://eslint.org/docs/developer-guide/nodejs-api#cliengine)
using standard webpack [loader options](https://webpack.js.org/configuration/module/#useentry).
Note that the config option you provide will be passed to the `CLIEngine`.
This is a different set of options than what you'd specify in `package.json` or `.eslintrc`.
See the [eslint docs](http://eslint.org/docs/developer-guide/nodejs-api#cliengine) for more detail.
#### `fix` (default: false)
This option will enable
[ESLint autofix feature](http://eslint.org/docs/user-guide/command-line-interface#fix).
**Be careful: this option will change source files.**
#### `cache` (default: false)
This option will enable caching of the linting results into a file.
This is particularly useful in reducing linting time when doing a full build.
This can either be a `boolean` value or the cache directory path(ex: `'./.eslint-loader-cache'`).
If `cache: true` is used, the cache file is written to the `./node_modules/.cache` directory.
This is the recommended usage.
#### `formatter` (default: eslint stylish formatter)
Loader accepts a function that will have one argument: an array of eslint messages (object).
The function must return the output as a string.
You can use official eslint formatters.
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
// several examples !
// default value
formatter: require("eslint/lib/formatters/stylish"),
// community formatter
formatter: require("eslint-friendly-formatter"),
// custom formatter
formatter: function(results) {
// `results` format is available here
// http://eslint.org/docs/developer-guide/nodejs-api.html#executeonfiles()
// you should return a string
// DO NOT USE console.*() directly !
return "OUTPUT";
}
}
}
]
}
};
```
#### `eslintPath` (default: "eslint")
Path to `eslint` instance that will be used for linting.
If the `eslintPath` is a folder like a official eslint, or specify a `formatter` option. now you dont have to install `eslint` .
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
eslintPath: path.join(__dirname, "reusable-eslint")
}
}
]
}
};
```
#### Errors and Warning
**By default the loader will auto adjust error reporting depending
on eslint errors/warnings counts.**
You can still force this behavior by using `emitError` **or** `emitWarning` options:
##### `emitError` (default: `false`)
Loader will always return errors if this option is set to `true`.
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
emitError: true
}
}
]
}
};
```
##### `emitWarning` (default: `false`)
Loader will always return warnings if option is set to `true`. If you're using hot module replacement, you may wish to enable this in development, or else updates will be skipped when there's an eslint error.
#### `quiet` (default: `false`)
Loader will process and report errors only and ignore warnings if this option is set to true
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
quiet: true
}
}
]
}
};
```
##### `failOnWarning` (default: `false`)
Loader will cause the module build to fail if there are any eslint warnings.
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
failOnWarning: true
}
}
]
}
};
```
##### `failOnError` (default: `false`)
Loader will cause the module build to fail if there are any eslint errors.
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
failOnError: true
}
}
]
}
};
```
##### `outputReport` (default: `false`)
Write the output of the errors to a file, for example a checkstyle xml file for use for reporting on Jenkins CI
The `filePath` is relative to the webpack config: output.path
You can pass in a different formatter for the output file, if none is passed in the default/configured formatter will be used
```js
module.exports = {
entry: "...",
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: "eslint-loader",
options: {
outputReport: {
filePath: "checkstyle.xml",
formatter: require("eslint/lib/formatters/checkstyle")
}
}
}
]
}
};
```
## Gotchas
### NoErrorsPlugin
`NoErrorsPlugin` prevents webpack from outputting anything into a bundle. So even ESLint warnings
will fail the build. No matter what error settings are used for `eslint-loader`.
So if you want to see ESLint warnings in console during development using `WebpackDevServer`
remove `NoErrorsPlugin` from webpack config.
### Defining `configFile` or using `eslint -c path/.eslintrc`
Bear in mind that when you define `configFile`, `eslint` doesn't automatically look for
`.eslintrc` files in the directory of the file to be linted.
More information is available in official eslint documentation in section [_Using Configuration Files_](http://eslint.org/docs/user-guide/configuring#using-configuration-files).
See [#129](https://github.com/webpack-contrib/eslint-loader/issues/129).
---
## Changelog
[Changelog](CHANGELOG.md)
## License
[MIT](./LICENSE)
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