eslint-loader

eslint loader for webpack

Install

$ npm install eslint-loader --save-dev

Usage

In your webpack configuration

module.exports = {
  // ...
  module: {
    loaders: [
      {test: /\.js$/, loader: "eslint-loader", exclude: /node_modules/}
    ]
  }
  // ...
}

When using with transpiling loaders (like babel-loader), make sure they are in correct order (bottom to top). Otherwise files will be check after being processed by babel-loader

module.exports = {
  // ...
  module: {
    loaders: [
      {test: /\.js$/, loaders: [ "babel-loader", "eslint-loader" ], exclude: /node_modules/},
    ]
  }
  // ...
}

To be safe, you can use preLoaders section to check source files, not modified by other loaders (like babel-loader)

module.exports = {
  // ...
  module: {
    preLoaders: [
      {test: /\.js$/, loader: "eslint-loader", exclude: /node_modules/}
    ]
  }
  // ...
}

webpack@2.1.0-beta.23 has breaking changes. preLoaders is removed from the webpack^{2.1.0-beta.23.} so move it to loaders and using [enforce: "pre"] instead.

module.exports = {
  // ...
  module: {
    loaders: [
      {enforce: "pre", test: /\.js$/,  loader: "eslint-loader", exclude: /node_modules/}
      // ... other loader
    ]
  }
  // ...
}

Options

You can pass eslint options directly by

• Adding a query string to the loader for this loader usage only

{
  module: {
    preLoaders: [
      {
        test: /\.js$/,
        loader: "eslint-loader?{rules:{semi:0}}",
        exclude: /node_modules/,
      },
    ],
  },
}

• Adding an eslint entry in your webpack config for global options:

module.exports = {
  eslint: {
    configFile: 'path/.eslintrc'
  }
}

Note that you can use both methods in order to benefit from global & specific options

fix (default: false)

This option will enable ESLint autofix feature.

Be careful, this option might cause webpack to enter an infinite build loop if some issues cannot be fixed properly.

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.

The cache file is written to the ./node_modules/.cache directory, thanks to the usage of the find-cache-dir module.

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.

module.exports = {
  entry: "...",
  module: {
    // ...
  }
  eslint: {
    // 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"
    }
  }
}

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.

module.exports = {
  entry: "...",
  module: {
    // ...
  },
  eslint: {
    emitError: true
  }
}

emitWarning (default: false)

Loader will always return warnings if option is set to true.

quiet (default: false)

Loader will process and report errors only and ignore warnings if this option is set to true

module.exports = {
  entry: "...",
  module: {
    // ...
  },
  eslint: {
    quiet: true
  }
}

failOnWarning (default: false)

Loader will cause the module build to fail if there are any eslint warnings.

module.exports = {
  entry: "...",
  module: {
    // ...
  },
  eslint: {
    failOnWarning: true
  }
}

failOnError (default: false)

Loader will cause the module build to fail if there are any eslint errors.

module.exports = {
  entry: "...",
  module: {
    // ...
  },
  eslint: {
    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

module.exports = {
  entry: "...",
  module: {
    // ...
  },
  eslint: {
    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.

Changelog

License