| 1 | <div align="center">
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| 2 | <a href="https://github.com/webpack/webpack">
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| 3 | <img width="200" height="200" src="https://webpack.js.org/assets/icon-square-big.svg">
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| 4 | </a>
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| 5 | </div>
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| 6 |
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| 7 | [![npm][npm]][npm-url]
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| 8 | [![node][node]][node-url]
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| 9 | [![deps][deps]][deps-url]
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| 10 | [![tests][tests]][tests-url]
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| 11 | [![cover][cover]][cover-url]
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| 12 | [![chat][chat]][chat-url]
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| 13 | [![size][size]][size-url]
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| 14 |
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| 15 | # less-loader
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| 16 |
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| 17 | A Less loader for webpack. Compiles Less to CSS.
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| 18 |
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| 19 | ## Getting Started
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| 20 |
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| 21 | To begin, you'll need to install `less` and `less-loader`:
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| 22 |
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| 23 | ```console
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| 24 | $ npm install less less-loader --save-dev
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| 25 | ```
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| 26 |
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| 27 | Then add the loader to your `webpack` config. For example:
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| 28 |
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| 29 | **webpack.config.js**
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| 30 |
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| 31 | ```js
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| 32 | module.exports = {
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| 33 | module: {
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| 34 | rules: [
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| 35 | {
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| 36 | test: /\.less$/i,
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| 37 | loader: [
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| 38 | // compiles Less to CSS
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| 39 | "style-loader",
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| 40 | "css-loader",
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| 41 | "less-loader",
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| 42 | ],
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| 43 | },
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| 44 | ],
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| 45 | },
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| 46 | };
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| 47 | ```
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| 48 |
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| 49 | And run `webpack` via your preferred method.
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| 50 |
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| 51 | ## Options
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| 52 |
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| 53 | | Name | Type | Default | Description |
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| 54 | | :---------------------------------------: | :------------------: | :----------------------: | :----------------------------------------------------- |
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| 55 | | **[`lessOptions`](#lessoptions)** | `{Object\|Function}` | `{ relativeUrls: true }` | Options for Less. |
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| 56 | | **[`additionalData`](#additionalData)** | `{String\|Function}` | `undefined` | Prepends/Appends `Less` code to the actual entry file. |
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| 57 | | **[`sourceMap`](#sourcemap)** | `{Boolean}` | `compiler.devtool` | Enables/Disables generation of source maps. |
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| 58 | | **[`webpackImporter`](#webpackimporter)** | `{Boolean}` | `true` | Enables/Disables the default Webpack importer. |
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| 59 | | **[`implementation`](#implementation)** | `{Object\|String}` | `less` | Setup Less implementation to use. |
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| 60 |
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| 61 | ### `lessOptions`
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| 62 |
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| 63 | Type: `Object|Function`
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| 64 | Default: `{ relativeUrls: true }`
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| 65 |
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| 66 | You can pass any Less specific options to the `less-loader` through the `lessOptions` property in the [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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| 67 |
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| 68 | #### `Object`
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| 69 |
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| 70 | Use an object to pass options through to Less.
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| 71 |
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| 72 | **webpack.config.js**
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| 73 |
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| 74 | ```js
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| 75 | module.exports = {
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| 76 | module: {
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| 77 | rules: [
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| 78 | {
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| 79 | test: /\.less$/i,
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| 80 | use: [
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| 81 | {
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| 82 | loader: "style-loader",
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| 83 | },
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| 84 | {
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| 85 | loader: "css-loader",
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| 86 | },
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| 87 | {
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| 88 | loader: "less-loader",
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| 89 | options: {
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| 90 | lessOptions: {
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| 91 | strictMath: true,
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| 92 | },
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| 93 | },
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| 94 | },
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| 95 | ],
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| 96 | },
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| 97 | ],
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| 98 | },
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| 99 | };
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| 100 | ```
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| 101 |
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| 102 | #### `Function`
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| 103 |
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| 104 | Allows setting the options passed through to Less based off of the loader context.
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| 105 |
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| 106 | ```js
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| 107 | module.exports = {
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| 108 | module: {
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| 109 | rules: [
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| 110 | {
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| 111 | test: /\.less$/i,
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| 112 | use: [
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| 113 | "style-loader",
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| 114 | "css-loader",
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| 115 | {
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| 116 | loader: "less-loader",
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| 117 | options: {
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| 118 | lessOptions: (loaderContext) => {
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| 119 | // More information about available properties https://webpack.js.org/api/loaders/
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| 120 | const { resourcePath, rootContext } = loaderContext;
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| 121 | const relativePath = path.relative(rootContext, resourcePath);
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| 122 |
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| 123 | if (relativePath === "styles/foo.less") {
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| 124 | return {
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| 125 | paths: ["absolute/path/c", "absolute/path/d"],
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| 126 | };
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| 127 | }
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| 128 |
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| 129 | return {
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| 130 | paths: ["absolute/path/a", "absolute/path/b"],
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| 131 | };
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| 132 | },
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| 133 | },
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| 134 | },
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| 135 | ],
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| 136 | },
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| 137 | ],
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| 138 | },
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| 139 | };
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| 140 | ```
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| 141 |
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| 142 | ### `additionalData`
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| 143 |
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| 144 | Type: `String|Function`
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| 145 | Default: `undefined`
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| 146 |
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| 147 | Prepends `Less` code before the actual entry file.
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| 148 | In this case, the `less-loader` will not override the source but just **prepend** the entry's content.
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| 149 |
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| 150 | This is especially useful when some of your Less variables depend on the environment:
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| 151 |
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| 152 | > ℹ Since you're injecting code, this will break the source mappings in your entry file. Often there's a simpler solution than this, like multiple Less entry files.
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| 153 |
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| 154 | #### `String`
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| 155 |
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| 156 | ```js
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| 157 | module.exports = {
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| 158 | module: {
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| 159 | rules: [
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| 160 | {
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| 161 | test: /\.less$/i,
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| 162 | use: [
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| 163 | "style-loader",
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| 164 | "css-loader",
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| 165 | {
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| 166 | loader: "less-loader",
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| 167 | options: {
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| 168 | additionalData: `@env: ${process.env.NODE_ENV};`,
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| 169 | },
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| 170 | },
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| 171 | ],
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| 172 | },
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| 173 | ],
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| 174 | },
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| 175 | };
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| 176 | ```
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| 177 |
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| 178 | #### `Function`
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| 179 |
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| 180 | ##### Sync
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| 181 |
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| 182 | ```js
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| 183 | module.exports = {
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| 184 | module: {
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| 185 | rules: [
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| 186 | {
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| 187 | test: /\.less$/i,
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| 188 | use: [
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| 189 | "style-loader",
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| 190 | "css-loader",
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| 191 | {
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| 192 | loader: "less-loader",
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| 193 | options: {
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| 194 | additionalData: (content, loaderContext) => {
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| 195 | // More information about available properties https://webpack.js.org/api/loaders/
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| 196 | const { resourcePath, rootContext } = loaderContext;
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| 197 | const relativePath = path.relative(rootContext, resourcePath);
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| 198 |
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| 199 | if (relativePath === "styles/foo.less") {
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| 200 | return "@value: 100px;" + content;
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| 201 | }
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| 202 |
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| 203 | return "@value: 200px;" + content;
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| 204 | },
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| 205 | },
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| 206 | },
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| 207 | ],
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| 208 | },
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| 209 | ],
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| 210 | },
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| 211 | };
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| 212 | ```
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| 213 |
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| 214 | ##### Async
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| 215 |
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| 216 | ```js
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| 217 | module.exports = {
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| 218 | module: {
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| 219 | rules: [
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| 220 | {
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| 221 | test: /\.less$/i,
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| 222 | use: [
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| 223 | "style-loader",
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| 224 | "css-loader",
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| 225 | {
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| 226 | loader: "less-loader",
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| 227 | options: {
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| 228 | additionalData: async (content, loaderContext) => {
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| 229 | // More information about available properties https://webpack.js.org/api/loaders/
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| 230 | const { resourcePath, rootContext } = loaderContext;
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| 231 | const relativePath = path.relative(rootContext, resourcePath);
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| 232 |
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| 233 | if (relativePath === "styles/foo.less") {
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| 234 | return "@value: 100px;" + content;
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| 235 | }
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| 236 |
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| 237 | return "@value: 200px;" + content;
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| 238 | },
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| 239 | },
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| 240 | },
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| 241 | ],
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| 242 | },
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| 243 | ],
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| 244 | },
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| 245 | };
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| 246 | ```
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| 247 |
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| 248 | ### `sourceMap`
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| 249 |
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| 250 | Type: `Boolean`
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| 251 | Default: depends on the `compiler.devtool` value
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| 252 |
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| 253 | By default generation of source maps depends on the [`devtool`](https://webpack.js.org/configuration/devtool/) option. All values enable source map generation except `eval` and `false` value.
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| 254 |
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| 255 | **webpack.config.js**
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| 256 |
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| 257 | ```js
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| 258 | module.exports = {
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| 259 | module: {
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| 260 | rules: [
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| 261 | {
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| 262 | test: /\.less$/i,
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| 263 | use: [
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| 264 | "style-loader",
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| 265 | {
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| 266 | loader: "css-loader",
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| 267 | options: {
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| 268 | sourceMap: true,
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| 269 | },
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| 270 | },
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| 271 | {
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| 272 | loader: "less-loader",
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| 273 | options: {
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| 274 | sourceMap: true,
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| 275 | },
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| 276 | },
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| 277 | ],
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| 278 | },
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| 279 | ],
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| 280 | },
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| 281 | };
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| 282 | ```
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| 283 |
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| 284 | ### `webpackImporter`
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| 285 |
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| 286 | Type: `Boolean`
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| 287 | Default: `true`
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| 288 |
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| 289 | Enables/Disables the default `webpack` importer.
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| 290 |
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| 291 | This can improve performance in some cases. Use it with caution because aliases and `@import` at-rules starting with `~` will not work.
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| 292 |
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| 293 | **webpack.config.js**
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| 294 |
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| 295 | ```js
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| 296 | module.exports = {
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| 297 | module: {
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| 298 | rules: [
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| 299 | {
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| 300 | test: /\.less$/i,
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| 301 | use: [
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| 302 | "style-loader",
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| 303 | "css-loader",
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| 304 | {
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| 305 | loader: "less-loader",
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| 306 | options: {
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| 307 | webpackImporter: false,
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| 308 | },
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| 309 | },
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| 310 | ],
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| 311 | },
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| 312 | ],
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| 313 | },
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| 314 | };
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| 315 | ```
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| 316 |
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| 317 | ### `implementation`
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| 318 |
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| 319 | Type: `Object | String`
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| 320 |
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| 321 | > ⚠ less-loader compatible with Less 3 and 4 versions
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| 322 |
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| 323 | The special `implementation` option determines which implementation of Less to use. Overrides the locally installed `peerDependency` version of `less`.
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| 324 |
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| 325 | **This option is only really useful for downstream tooling authors to ease the Less 3-to-4 transition.**
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| 326 |
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| 327 | #### Object
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| 328 |
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| 329 | **webpack.config.js**
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| 330 |
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| 331 | ```js
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| 332 | module.exports = {
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| 333 | module: {
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| 334 | rules: [
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| 335 | {
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| 336 | test: /\.less$/i,
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| 337 | use: [
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| 338 | "style-loader",
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| 339 | "css-loader",
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| 340 | {
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| 341 | loader: "less-loader",
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| 342 | options: {
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| 343 | implementation: require("less"),
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| 344 | },
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| 345 | },
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| 346 | ],
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| 347 | },
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| 348 | ],
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| 349 | },
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| 350 | };
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| 351 | ```
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| 352 |
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| 353 | #### String
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| 354 |
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| 355 | **webpack.config.js**
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| 356 |
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| 357 | ```js
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| 358 | module.exports = {
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| 359 | module: {
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| 360 | rules: [
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| 361 | {
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| 362 | test: /\.less$/i,
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| 363 | use: [
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| 364 | "style-loader",
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| 365 | "css-loader",
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| 366 | {
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| 367 | loader: "less-loader",
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| 368 | options: {
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| 369 | implementation: require.resolve("less"),
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| 370 | },
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| 371 | },
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| 372 | ],
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| 373 | },
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| 374 | ],
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| 375 | },
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| 376 | };
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| 377 | ```
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| 378 |
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| 379 | ## Examples
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| 380 |
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| 381 | ### Normal usage
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| 382 |
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| 383 | 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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| 384 |
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| 385 | **webpack.config.js**
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| 386 |
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| 387 | ```js
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| 388 | module.exports = {
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| 389 | module: {
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| 390 | rules: [
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| 391 | {
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| 392 | test: /\.less$/i,
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| 393 | use: [
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| 394 | {
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| 395 | loader: "style-loader", // creates style nodes from JS strings
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| 396 | },
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| 397 | {
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| 398 | loader: "css-loader", // translates CSS into CommonJS
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| 399 | },
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| 400 | {
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| 401 | loader: "less-loader", // compiles Less to CSS
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| 402 | },
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| 403 | ],
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| 404 | },
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| 405 | ],
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| 406 | },
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| 407 | };
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| 408 | ```
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| 409 |
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| 410 | Unfortunately, Less doesn't map all options 1-by-1 to camelCase. When in doubt, [check their executable](https://github.com/less/less.js/blob/3.x/bin/lessc) and search for the dash-case option.
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| 411 |
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| 412 | ### Source maps
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| 413 |
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| 414 | To enable sourcemaps for CSS, you'll need to pass the `sourceMap` property in the loader's options. If this is not passed, the loader will respect the setting for webpack source maps, set in `devtool`.
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| 415 |
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| 416 | **webpack.config.js**
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| 417 |
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| 418 | ```js
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| 419 | module.exports = {
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| 420 | devtool: "source-map", // any "source-map"-like devtool is possible
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| 421 | module: {
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| 422 | rules: [
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| 423 | {
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| 424 | test: /\.less$/i,
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| 425 | use: [
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| 426 | "style-loader",
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| 427 | {
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| 428 | loader: "css-loader",
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| 429 | options: {
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| 430 | sourceMap: true,
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| 431 | },
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| 432 | },
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| 433 | {
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| 434 | loader: "less-loader",
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| 435 | options: {
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| 436 | sourceMap: true,
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| 437 | },
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| 438 | },
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| 439 | ],
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| 440 | },
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| 441 | ],
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| 442 | },
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| 443 | };
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| 444 | ```
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| 445 |
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| 446 | 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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| 447 |
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| 448 | ### In production
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| 449 |
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| 450 | Usually, it's recommended to extract the style sheets into a dedicated file in production using the [MiniCssExtractPlugin](https://github.com/webpack-contrib/mini-css-extract-plugin). This way your styles are not dependent on JavaScript.
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| 451 |
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| 452 | ### Imports
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| 453 |
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| 454 | First we try to use built-in `less` resolve logic, then `webpack` resolve logic (aliases and `~`).
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| 455 |
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| 456 | #### Webpack Resolver
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| 457 |
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| 458 | `webpack` provides an [advanced mechanism to resolve files](https://webpack.js.org/configuration/resolve/).
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| 459 | `less-loader` applies a Less plugin that passes all queries to the webpack resolver if `less` could not resolve `@import`.
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| 460 | Thus you can import your Less modules from `node_modules`.
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| 461 |
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| 462 | ```css
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| 463 | @import "bootstrap/less/bootstrap";
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| 464 | ```
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| 465 |
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| 466 | Using `~` is deprecated and can be removed from your code (**we recommend it**), but we still support it for historical reasons.
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| 467 | Why you can removed it? The loader will first try to resolve `@import` as relative, if it cannot be resolved, the loader will try to resolve `@import` inside [`node_modules`](https://webpack.js.org/configuration/resolve/#resolve-modules).
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| 468 | 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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| 469 |
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| 470 | ```css
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| 471 | @import "~bootstrap/less/bootstrap";
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| 472 | ```
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| 473 |
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| 474 | Default resolver options can be modified by [`resolve.byDependency`](https://webpack.js.org/configuration/resolve/#resolvebydependency):
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| 475 |
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| 476 | **webpack.config.js**
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| 477 |
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| 478 | ```js
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| 479 | module.exports = {
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| 480 | devtool: "source-map", // any "source-map"-like devtool is possible
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| 481 | module: {
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| 482 | rules: [
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| 483 | {
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| 484 | test: /\.less$/i,
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| 485 | use: ["style-loader", "css-loader", "less-loader"],
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| 486 | },
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| 487 | ],
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| 488 | },
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| 489 | resolve: {
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| 490 | byDependency: {
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| 491 | // More options can be found here https://webpack.js.org/configuration/resolve/
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| 492 | less: {
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| 493 | mainFiles: ["custom"],
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| 494 | },
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| 495 | },
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| 496 | },
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| 497 | };
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| 498 | ```
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| 499 |
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| 500 | 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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| 501 |
|
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| 502 | #### Less Resolver
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| 503 |
|
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| 504 | If you specify the `paths` option, modules will be searched in the given `paths`. This is `less` default behavior. `paths` should be an array with absolute paths:
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| 505 |
|
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| 506 | **webpack.config.js**
|
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| 507 |
|
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| 508 | ```js
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| 509 | module.exports = {
|
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| 510 | module: {
|
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| 511 | rules: [
|
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| 512 | {
|
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| 513 | test: /\.less$/i,
|
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| 514 | use: [
|
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| 515 | {
|
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| 516 | loader: "style-loader",
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| 517 | },
|
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| 518 | {
|
|---|
| 519 | loader: "css-loader",
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| 520 | },
|
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| 521 | {
|
|---|
| 522 | loader: "less-loader",
|
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| 523 | options: {
|
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| 524 | lessOptions: {
|
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| 525 | paths: [path.resolve(__dirname, "node_modules")],
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| 526 | },
|
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| 527 | },
|
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| 528 | },
|
|---|
| 529 | ],
|
|---|
| 530 | },
|
|---|
| 531 | ],
|
|---|
| 532 | },
|
|---|
| 533 | };
|
|---|
| 534 | ```
|
|---|
| 535 |
|
|---|
| 536 | ### Plugins
|
|---|
| 537 |
|
|---|
| 538 | In order to use [plugins](http://lesscss.org/usage/#plugins), simply set the `plugins` option like this:
|
|---|
| 539 |
|
|---|
| 540 | **webpack.config.js**
|
|---|
| 541 |
|
|---|
| 542 | ```js
|
|---|
| 543 | const CleanCSSPlugin = require('less-plugin-clean-css');
|
|---|
| 544 |
|
|---|
| 545 | module.exports = {
|
|---|
| 546 | ...
|
|---|
| 547 | {
|
|---|
| 548 | loader: 'less-loader',
|
|---|
| 549 | options: {
|
|---|
| 550 | lessOptions: {
|
|---|
| 551 | plugins: [
|
|---|
| 552 | new CleanCSSPlugin({ advanced: true }),
|
|---|
| 553 | ],
|
|---|
| 554 | },
|
|---|
| 555 | },
|
|---|
| 556 | },
|
|---|
| 557 | ...
|
|---|
| 558 | };
|
|---|
| 559 | ```
|
|---|
| 560 |
|
|---|
| 561 | > ℹ️ Access to the [loader context](https://webpack.js.org/api/loaders/#the-loader-context) inside the custom plugin can be done using the `pluginManager.webpackLoaderContext` property.
|
|---|
| 562 |
|
|---|
| 563 | ```js
|
|---|
| 564 | module.exports = {
|
|---|
| 565 | install: function (less, pluginManager, functions) {
|
|---|
| 566 | functions.add("pi", function () {
|
|---|
| 567 | // Loader context is available in `pluginManager.webpackLoaderContext`
|
|---|
| 568 |
|
|---|
| 569 | return Math.PI;
|
|---|
| 570 | });
|
|---|
| 571 | },
|
|---|
| 572 | };
|
|---|
| 573 | ```
|
|---|
| 574 |
|
|---|
| 575 | ### Extracting style sheets
|
|---|
| 576 |
|
|---|
| 577 | 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.
|
|---|
| 578 |
|
|---|
| 579 | There are two possibilities to extract a style sheet from the bundle:
|
|---|
| 580 |
|
|---|
| 581 | - [`extract-loader`](https://github.com/peerigon/extract-loader) (simpler, but specialized on the css-loader's output)
|
|---|
| 582 | - [MiniCssExtractPlugin](https://github.com/webpack-contrib/mini-css-extract-plugin) (more complex, but works in all use-cases)
|
|---|
| 583 |
|
|---|
| 584 | ### CSS modules gotcha
|
|---|
| 585 |
|
|---|
| 586 | 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).
|
|---|
| 587 |
|
|---|
| 588 | ## Contributing
|
|---|
| 589 |
|
|---|
| 590 | Please take a moment to read our contributing guidelines if you haven't yet done so.
|
|---|
| 591 |
|
|---|
| 592 | [CONTRIBUTING](./.github/CONTRIBUTING.md)
|
|---|
| 593 |
|
|---|
| 594 | ## License
|
|---|
| 595 |
|
|---|
| 596 | [MIT](./LICENSE)
|
|---|
| 597 |
|
|---|
| 598 | [npm]: https://img.shields.io/npm/v/less-loader.svg
|
|---|
| 599 | [npm-url]: https://npmjs.com/package/less-loader
|
|---|
| 600 | [node]: https://img.shields.io/node/v/less-loader.svg
|
|---|
| 601 | [node-url]: https://nodejs.org
|
|---|
| 602 | [deps]: https://david-dm.org/webpack-contrib/less-loader.svg
|
|---|
| 603 | [deps-url]: https://david-dm.org/webpack-contrib/less-loader
|
|---|
| 604 | [tests]: https://github.com/webpack-contrib/less-loader/workflows/less-loader/badge.svg
|
|---|
| 605 | [tests-url]: https://github.com/webpack-contrib/less-loader/actions
|
|---|
| 606 | [cover]: https://codecov.io/gh/webpack-contrib/less-loader/branch/master/graph/badge.svg
|
|---|
| 607 | [cover-url]: https://codecov.io/gh/webpack-contrib/less-loader
|
|---|
| 608 | [chat]: https://img.shields.io/badge/gitter-webpack%2Fwebpack-brightgreen.svg
|
|---|
| 609 | [chat-url]: https://gitter.im/webpack/webpack
|
|---|
| 610 | [size]: https://packagephobia.now.sh/badge?p=less-loader
|
|---|
| 611 | [size-url]: https://packagephobia.now.sh/result?p=less-loader
|
|---|
