Icard/angular-clarity-master(work.../node_modules/less-loader/README.md

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# less-loader
A Less loader for webpack. Compiles Less to CSS.
## Getting Started
To begin, you'll need to install `less` and `less-loader`:
```console
npm install less less-loader --save-dev
```
or
```console
yarn add -D less less-loader
```
or
```console
pnpm add -D less less-loader
```
Then add the loader to your `webpack` config. For example:
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
// compiles Less to CSS
"style-loader",
"css-loader",
"less-loader",
],
},
],
},
};
```
And run `webpack` via your preferred method.
## Options
- **[`lessOptions`](#lessoptions)**
- **[`additionalData`](#additionalData)**
- **[`sourceMap`](#sourcemap)**
- **[`webpackImporter`](#webpackimporter)**
- **[`implementation`](#implementation)**
### `lessOptions`
Type:
```ts
type lessOptions = import('less').options | ((loaderContext: LoaderContext) => import('less').options})
```
Default: `{ relativeUrls: true }`
You can pass any Less specific options to the `less-loader` through the `lessOptions` property in the [loader options](https://webpack.js.org/configuration/module/#rule-options-rule-query). See the [Less documentation](http://lesscss.org/usage/#command-line-usage-options) for all available options in dash-case. Since we're passing these options to Less programmatically, you need to pass them in camelCase here:
#### `object`
Use an object to pass options through to Less.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
{
loader: "style-loader",
},
{
loader: "css-loader",
},
{
loader: "less-loader",
options: {
lessOptions: {
strictMath: true,
},
},
},
],
},
],
},
};
```
#### `function`
Allows setting the options passed through to Less based off of the loader context.
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
lessOptions: (loaderContext) => {
// More information about available properties https://webpack.js.org/api/loaders/
const { resourcePath, rootContext } = loaderContext;
const relativePath = path.relative(rootContext, resourcePath);
if (relativePath === "styles/foo.less") {
return {
paths: ["absolute/path/c", "absolute/path/d"],
};
}
return {
paths: ["absolute/path/a", "absolute/path/b"],
};
},
},
},
],
},
],
},
};
```
### `additionalData`
Type:
```ts
type additionalData =
| string
| ((content: string, loaderContext: LoaderContext) => string);
```
Default: `undefined`
Prepends/Appends `Less` code to the actual entry file.
In this case, the `less-loader` will not override the source but just **prepend** the entry's content.
This is especially useful when some of your Less variables depend on the environment:
> Since you're injecting code, this will break the source mappings in your entry file. Often there's a simpler solution than this, like multiple Less entry files.
#### `string`
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
additionalData: `@env: ${process.env.NODE_ENV};`,
},
},
],
},
],
},
};
```
#### `function`
##### `Sync`
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
additionalData: (content, loaderContext) => {
// More information about available properties https://webpack.js.org/api/loaders/
const { resourcePath, rootContext } = loaderContext;
const relativePath = path.relative(rootContext, resourcePath);
if (relativePath === "styles/foo.less") {
return "@value: 100px;" + content;
}
return "@value: 200px;" + content;
},
},
},
],
},
],
},
};
```
##### `Async`
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
additionalData: async (content, loaderContext) => {
// More information about available properties https://webpack.js.org/api/loaders/
const { resourcePath, rootContext } = loaderContext;
const relativePath = path.relative(rootContext, resourcePath);
if (relativePath === "styles/foo.less") {
return "@value: 100px;" + content;
}
return "@value: 200px;" + content;
},
},
},
],
},
],
},
};
```
### `sourceMap`
Type:
```ts
type sourceMap = boolean;
```
Default: depends on the `compiler.devtool` value
By default generation of source maps depends on the [`devtool`](https://webpack.js.org/configuration/devtool/) option. All values enable source map generation except `eval` and `false` value.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
{
loader: "css-loader",
options: {
sourceMap: true,
},
},
{
loader: "less-loader",
options: {
sourceMap: true,
},
},
],
},
],
},
};
```
### `webpackImporter`
Type:
```ts
type webpackImporter = boolean;
```
Default: `true`
Enables/Disables the default `webpack` importer.
This can improve performance in some cases. Use it with caution because aliases and `@import` from [`node_modules`](https://webpack.js.org/configuration/resolve/#resolvemodules) will not work.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
webpackImporter: false,
},
},
],
},
],
},
};
```
### `implementation`
Type:
```ts
type implementation = object | string;
```
> less-loader compatible with Less 3 and 4 versions
The special `implementation` option determines which implementation of Less to use. Overrides the locally installed `peerDependency` version of `less`.
**This option is only really useful for downstream tooling authors to ease the Less 3-to-4 transition.**
#### `object`
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
implementation: require("less"),
},
},
],
},
],
},
};
```
#### `string`
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
"css-loader",
{
loader: "less-loader",
options: {
implementation: require.resolve("less"),
},
},
],
},
],
},
};
```
## Examples
### Normal usage
Chain the `less-loader` with the [`css-loader`](https://github.com/webpack-contrib/css-loader) and the [`style-loader`](https://github.com/webpack-contrib/style-loader) to immediately apply all styles to the DOM.
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
{
loader: "style-loader", // creates style nodes from JS strings
},
{
loader: "css-loader", // translates CSS into CommonJS
},
{
loader: "less-loader", // compiles Less to CSS
},
],
},
],
},
};
```
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.
### Source maps
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`.
**webpack.config.js**
```js
module.exports = {
devtool: "source-map", // any "source-map"-like devtool is possible
module: {
rules: [
{
test: /\.less$/i,
use: [
"style-loader",
{
loader: "css-loader",
options: {
sourceMap: true,
},
},
{
loader: "less-loader",
options: {
sourceMap: true,
},
},
],
},
],
},
};
```
If you want to edit the original Less files inside Chrome, [there's a good blog post](https://medium.com/@toolmantim/getting-started-with-css-sourcemaps-and-in-browser-sass-editing-b4daab987fb0). The blog post is about Sass but it also works for Less.
### In production
Usually, it's recommended to extract the style sheets into a dedicated file in production using the [MiniCssExtractPlugin](https://github.com/webpack-contrib/mini-css-extract-plugin). This way your styles are not dependent on JavaScript.
### Imports
First we try to use built-in `less` resolve logic, then `webpack` resolve logic.
#### Webpack Resolver
`webpack` provides an [advanced mechanism to resolve files](https://webpack.js.org/configuration/resolve/).
`less-loader` applies a Less plugin that passes all queries to the webpack resolver if `less` could not resolve `@import`.
Thus you can import your Less modules from `node_modules`.
```css
@import "bootstrap/less/bootstrap";
```
Using `~` is deprecated and can be removed from your code (**we recommend it**), but we still support it for historical reasons.
Why you can removed it? The loader will first try to resolve `@import` as relative, if it cannot be resolved, the loader will try to resolve `@import` inside [`node_modules`](https://webpack.js.org/configuration/resolve/#resolvemodules).
Default resolver options can be modified by [`resolve.byDependency`](https://webpack.js.org/configuration/resolve/#resolvebydependency):
**webpack.config.js**
```js
module.exports = {
devtool: "source-map", // any "source-map"-like devtool is possible
module: {
rules: [
{
test: /\.less$/i,
use: ["style-loader", "css-loader", "less-loader"],
},
],
},
resolve: {
byDependency: {
// More options can be found here https://webpack.js.org/configuration/resolve/
less: {
mainFiles: ["custom"],
},
},
},
};
```
#### Less Resolver
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:
**webpack.config.js**
```js
module.exports = {
module: {
rules: [
{
test: /\.less$/i,
use: [
{
loader: "style-loader",
},
{
loader: "css-loader",
},
{
loader: "less-loader",
options: {
lessOptions: {
paths: [path.resolve(__dirname, "node_modules")],
},
},
},
],
},
],
},
};
```
### Plugins
In order to use [plugins](http://lesscss.org/usage/#plugins), simply set the `plugins` option like this:
**webpack.config.js**
```js
const CleanCSSPlugin = require('less-plugin-clean-css');
module.exports = {
...
{
loader: 'less-loader',
options: {
lessOptions: {
plugins: [
new CleanCSSPlugin({ advanced: true }),
],
},
},
},
...
};
```
> **Note**
>
> 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.
```js
module.exports = {
install: function (less, pluginManager, functions) {
functions.add("pi", function () {
// Loader context is available in `pluginManager.webpackLoaderContext`
return Math.PI;
});
},
};
```
### Extracting style sheets
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.
There are two possibilities to extract a style sheet from the bundle:
- [`extract-loader`](https://github.com/peerigon/extract-loader) (simpler, but specialized on the css-loader's output)
- [`MiniCssExtractPlugin`](https://github.com/webpack-contrib/mini-css-extract-plugin) (more complex, but works in all use-cases)
### CSS modules gotcha
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).
## Contributing
Please take a moment to read our contributing guidelines if you haven't yet done so.
[CONTRIBUTING](./.github/CONTRIBUTING.md)
## License
[MIT](./LICENSE)
[npm]: https://img.shields.io/npm/v/less-loader.svg
[npm-url]: https://npmjs.com/package/less-loader
[node]: https://img.shields.io/node/v/less-loader.svg
[node-url]: https://nodejs.org
[tests]: https://github.com/webpack-contrib/less-loader/workflows/less-loader/badge.svg
[tests-url]: https://github.com/webpack-contrib/less-loader/actions
[cover]: https://codecov.io/gh/webpack-contrib/less-loader/branch/master/graph/badge.svg
[cover-url]: https://codecov.io/gh/webpack-contrib/less-loader
[chat]: https://img.shields.io/badge/gitter-webpack%2Fwebpack-brightgreen.svg
[chat-url]: https://gitter.im/webpack/webpack
[size]: https://packagephobia.now.sh/badge?p=less-loader
[size-url]: https://packagephobia.now.sh/result?p=less-loader