JarCasting
eslint-loader
A ESlint loader for webpack
⚠️
DEPRECATED
eslint-loader has been deprecated. Please use eslint-webpack-plugin.
Install
npm install eslint-loader --save-dev
Note: You also need to install eslint from npm, if you haven't already:
npm install eslint --save-dev
Usage
In your webpack configuration:
module.exports = {
// ...
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
// eslint options (if necessary)
},
},
],
},
// ...
};
When using with transpiling loaders (like babel-loader), make sure they are in correct order (bottom to top). Otherwise files will be checked after being processed by babel-loader:
module.exports = {
// ...
module: {
rules: [
{
test: /\.js$/,
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):
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 using standard webpack loader options.
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 for more detail.
cache
- Type:
Boolean|String - 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 is written to the ./node_modules/.cache/eslint-loader directory. This is the recommended usage.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
cache: true,
},
},
],
},
};
eslintPath
- Type:
String - Default:
eslint
Path to eslint instance that will be used for linting. If the eslintPath is a folder like a official eslint, or specify a formatter option. Now you dont have to install eslint.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
eslintPath: path.join(__dirname, 'reusable-eslint'),
},
},
],
},
};
fix
- Type:
Boolean - Default:
false
This option will enable ESLint autofix feature.
Be careful: this option will change source files.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
fix: true,
},
},
],
},
};
formatter
- Type:
String|Function - Default:
stylish
This option accepts a function that will have one argument: an array of eslint messages (object). The function must return the output as a string. You can use official eslint formatters.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
// several examples !
// default value
formatter: '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
- Type:
Boolean - Default:
false
Will always return errors, if this option is set to true.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
emitError: true,
},
},
],
},
};
emitWarning
- Type:
Boolean - Default:
false
Will always return warnings, if option is set to true. If you're using hot module replacement, you may wish to enable this in development, or else updates will be skipped when there's an eslint error.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
emitWarning: true,
},
},
],
},
};
failOnError
- Type:
Boolean - Default:
false
Will cause the module build to fail if there are any errors, if option is set to true.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
failOnError: true,
},
},
],
},
};
failOnWarning
- Type:
Boolean - Default:
false
Will cause the module build to fail if there are any warnings, if option is set to true.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
failOnWarning: true,
},
},
],
},
};
quiet
- Type:
Boolean - Default:
false
Will process and report errors only and ignore warnings, if this option is set to true.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
quiet: true,
},
},
],
},
};
outputReport
- Type:
Boolean|Object - Default:
false
Write the output of the errors to a file, for example a checkstyle xml file for use for reporting on Jenkins CI.
The filePath is an absolute path or relative to the webpack config: output.path. You can pass in a different formatter for the output file, if none is passed in the default/configured formatter will be used.
module.exports = {
entry: '...',
module: {
rules: [
{
test: /\.js$/,
exclude: /node_modules/,
loader: 'eslint-loader',
options: {
outputReport: {
filePath: 'checkstyle.xml',
formatter: 'checkstyle',
},
},
},
],
},
};
Gotchas
NoEmitOnErrorsPlugin
NoEmitOnErrorsPlugin is now automatically enabled in webpack 4, when mode is either unset, or set to production. So even ESLint warnings will fail the build. No matter what error settings are used for eslint-loader, except if emitWarning enabled.
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. See #129.