280 lines
9.8 KiB
Markdown
280 lines
9.8 KiB
Markdown
[![npm][npm]][npm-url]
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[![node][node]][node-url]
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[![npm-stats][npm-stats]][npm-url]
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[![deps][deps]][deps-url]
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[![travis][travis]][travis-url]
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[![appveyor][appveyor]][appveyor-url]
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[![coverage][coverage]][coverage-url]
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[![chat][chat]][chat-url]
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<div align="center">
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<img width="200" height="200"
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src="https://cdn.worldvectorlogo.com/logos/less-63.svg">
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<a href="https://github.com/webpack/webpack">
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<img width="200" height="200"
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src="https://webpack.js.org/assets/icon-square-big.svg">
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</a>
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</div>
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<h1 align="center">less-loader</h1>
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<p align="center">Compiles Less to CSS.</p>
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Use the [`css-loader`](https://github.com/webpack-contrib/css-loader) or the [`raw-loader`](https://github.com/webpack-contrib/raw-loader) to turn it into a JS module and the [ExtractTextPlugin](https://github.com/webpack-contrib/extract-text-webpack-plugin) to extract it into a separate file.
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<h2 align="center">Install</h2>
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```bash
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npm install --save-dev less-loader less
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```
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The `less-loader` requires [less](https://github.com/less/less.js) as [`peerDependency`](https://docs.npmjs.com/files/package.json#peerdependencies). Thus you are able to control the versions accurately.
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<h2 align="center">Examples</h2>
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Chain the `less-loader` with the [`css-loader`](https://github.com/webpack-contrib/css-loader) and the [`style-loader`](https://github.com/webpack-contrib/style-loader) to immediately apply all styles to the DOM.
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```js
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// webpack.config.js
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.less$/,
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use: [{
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loader: "style-loader" // creates style nodes from JS strings
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}, {
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loader: "css-loader" // translates CSS into CommonJS
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}, {
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loader: "less-loader" // compiles Less to CSS
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}]
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}]
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}
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};
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```
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You can pass any Less specific options to the `less-loader` via [loader options](https://webpack.js.org/configuration/module/#rule-options-rule-query). See the [Less documentation](http://lesscss.org/usage/#command-line-usage-options) for all available options in dash-case. Since we're passing these options to Less programmatically, you need to pass them in camelCase here:
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```js
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// webpack.config.js
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.less$/,
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use: [{
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loader: "style-loader"
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}, {
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loader: "css-loader"
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}, {
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loader: "less-loader", options: {
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strictMath: true,
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noIeCompat: true
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}
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}]
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}]
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}
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};
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```
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Unfortunately, Less doesn't map all options 1-by-1 to camelCase. When in doubt, [check their executable and search for the dash-case option](https://github.com/less/less.js/blob/3.x/bin/lessc).
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### In production
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Usually, it's recommended to extract the style sheets into a dedicated file in production using the [ExtractTextPlugin](https://github.com/webpack-contrib/extract-text-webpack-plugin). This way your styles are not dependent on JavaScript:
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```js
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const ExtractTextPlugin = require("extract-text-webpack-plugin");
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const extractLess = new ExtractTextPlugin({
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filename: "[name].[contenthash].css",
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disable: process.env.NODE_ENV === "development"
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});
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.less$/,
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use: extractLess.extract({
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use: [{
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loader: "css-loader"
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}, {
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loader: "less-loader"
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}],
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// use style-loader in development
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fallback: "style-loader"
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})
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}]
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},
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plugins: [
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extractLess
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]
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};
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```
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<h2 align="center">Usage</h2>
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### Imports
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Starting with `less-loader` 4, you can now choose between Less' builtin resolver and webpack's resolver. By default, webpack's resolver is used.
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#### webpack resolver
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webpack provides an [advanced mechanism to resolve files](https://webpack.js.org/configuration/resolve/). The `less-loader` applies a Less plugin that passes all queries to the webpack resolver. Thus you can import your Less modules from `node_modules`. Just prepend them with a `~` which tells webpack to look up the [`modules`](https://webpack.js.org/configuration/resolve/#resolve-modules).
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```css
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@import "~bootstrap/less/bootstrap";
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```
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It's important to only prepend it with `~`, because `~/` resolves to the home-directory. webpack needs to distinguish between `bootstrap` and `~bootstrap`, because CSS and Less files have no special syntax for importing relative files. Writing `@import "file"` is the same as `@import "./file";`
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##### Non-Less imports
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Using webpack's resolver, you can import any file type. You just need a loader that exports valid Less code. Often, you will also want to set the `issuer` condition to ensure that this rule is only applied on imports originating from Less files:
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```js
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// webpack.config.js
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.js$/,
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issuer: /\.less$/,
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use: [{
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loader: "js-to-less-loader"
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}]
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}]
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}
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};
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```
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#### Less resolver
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If you specify the `paths` option, the `less-loader` will not use webpack's resolver. Modules, that can't be resolved in the local folder, will be searched in the given `paths`. This is Less' default behavior. `paths` should be an array with absolute paths:
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```js
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// webpack.config.js
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.less$/,
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use: [{
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loader: "style-loader"
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}, {
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loader: "css-loader"
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}, {
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loader: "less-loader", options: {
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paths: [
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path.resolve(__dirname, "node_modules")
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]
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}
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}]
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}]
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}
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};
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```
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In this case, all webpack features like importing non-Less files or aliasing won't work of course.
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### Plugins
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In order to use [plugins](http://lesscss.org/usage/#plugins), simply set the `plugins` option like this:
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```js
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// webpack.config.js
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const CleanCSSPlugin = require("less-plugin-clean-css");
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module.exports = {
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...
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{
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loader: "less-loader", options: {
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plugins: [
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new CleanCSSPlugin({ advanced: true })
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]
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}
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}]
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...
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};
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```
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### Extracting style sheets
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Bundling CSS with webpack has some nice advantages like referencing images and fonts with hashed urls or [hot module replacement](https://webpack.js.org/concepts/hot-module-replacement/) in development. In production, on the other hand, it's not a good idea to apply your style sheets depending on JS execution. Rendering may be delayed or even a [FOUC](https://en.wikipedia.org/wiki/Flash_of_unstyled_content) might be visible. Thus it's often still better to have them as separate files in your final production build.
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There are two possibilities to extract a style sheet from the bundle:
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- [`extract-loader`](https://github.com/peerigon/extract-loader) (simpler, but specialized on the css-loader's output)
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- [`ExtractTextWebpackPlugin`](https://github.com/webpack-contrib/extract-text-webpack-plugin) (more complex, but works in all use-cases)
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### Source maps
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To enable CSS source maps, you'll need to pass the `sourceMap` option to the `less-loader` *and* the `css-loader`. Your `webpack.config.js` should look like this:
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```javascript
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module.exports = {
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...
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module: {
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rules: [{
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test: /\.less$/,
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use: [{
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loader: "style-loader"
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}, {
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loader: "css-loader", options: {
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sourceMap: true
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}
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}, {
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loader: "less-loader", options: {
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sourceMap: true
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}
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}]
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}]
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}
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};
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```
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Also checkout the [sourceMaps example](https://github.com/webpack-contrib/less-loader/tree/master/examples/sourceMaps).
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If you want to edit the original Less files inside Chrome, [there's a good blog post](https://medium.com/@toolmantim/getting-started-with-css-sourcemaps-and-in-browser-sass-editing-b4daab987fb0). The blog post is about Sass but it also works for Less.
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### CSS modules gotcha
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There is a known problem with Less and [CSS modules](https://github.com/css-modules/css-modules) regarding relative file paths in `url(...)` statements. [See this issue for an explanation](https://github.com/webpack-contrib/less-loader/issues/109#issuecomment-253797335).
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<h2 align="center">Maintainer</h2>
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<table>
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<tr>
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<td align="center">
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<a href="https://github.com/jhnns"><img width="150" height="150" src="https://github.com/jhnns.png?s=150"></a>
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<br>
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<a href="https://github.com/jhnns">Johannes Ewald</a>
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</td>
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<tr>
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</table>
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[npm]: https://img.shields.io/npm/v/less-loader.svg
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[npm-stats]: https://img.shields.io/npm/dm/less-loader.svg
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[npm-url]: https://npmjs.com/package/less-loader
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[node]: https://img.shields.io/node/v/less-loader.svg
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[node-url]: https://nodejs.org
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[deps]: https://david-dm.org/webpack-contrib/less-loader.svg
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[deps-url]: https://david-dm.org/webpack-contrib/less-loader
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[travis]: http://img.shields.io/travis/webpack-contrib/less-loader.svg
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[travis-url]: https://travis-ci.org/webpack-contrib/less-loader
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[appveyor-url]: https://ci.appveyor.com/project/jhnns/less-loader/branch/master
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[appveyor]: https://ci.appveyor.com/api/projects/status/github/webpack-contrib/less-loader?svg=true
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[coverage]: https://img.shields.io/codecov/c/github/webpack-contrib/less-loader.svg
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[coverage-url]: https://codecov.io/gh/webpack-contrib/less-loader
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[chat]: https://badges.gitter.im/webpack-contrib/webpack.svg
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[chat-url]: https://gitter.im/webpack-contrib/webpack
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