ELRIWebSystem/Learning/vue/webpack/docs/pre-processors.md

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# Pre-Processors
This boilerplate has pre-configured CSS extraction for most popular CSS pre-processors including LESS, SASS, Stylus, and PostCSS. To use a pre-processor, all you need to do is install the appropriate webpack loader for it. For example, to use SASS:
``` bash
npm install sass-loader node-sass --save-dev
```
Note you also need to install `node-sass` because `sass-loader` depends on it as a peer dependency.
### Using Pre-Processors inside Components
Once installed, you can use the pre-processors inside your `*.vue` components using the `lang` attribute on `<style>` tags:
``` html
<style lang="scss">
/* write SASS! */
</style>
```
### A note on SASS syntax
- `lang="scss"` corresponds to the CSS-superset syntax (with curly braces and semicolons).
- `lang="sass"` corresponds to the indentation-based syntax.
### PostCSS
Styles in `*.vue` files and style files (`*.css`, `*.scss` etc) are piped through PostCSS by default, so you don't need to use a specific loader for it.
You can simply add PostCSS plugins you want to use to the `.postcssrc.js`file in your project's root directory:
``` js
// https://github.com/michael-ciniawsky/postcss-load-config
module.exports = {
"plugins": {
// to edit target browsers: use "browserslist" field in package.json
"postcss-import": {},
"autoprefixer": {}
}
}
```
See [vue-loader's related documentation](http://vuejs.github.io/vue-loader/en/features/postcss.html) for more details.
### Standalone CSS Files
To ensure consistent extraction and processing, it is recommended to import global, standalone style files from your root `App.vue` component, for example:
``` html
<!-- App.vue -->
<style src="./styles/global.less" lang="less"></style>
```
Note you should probably only do this for the styles written by yourself for your application. For existing libraries e.g. Bootstrap or Semantic UI, you can place them inside `/static` and reference them directly in `index.html`. This avoids extra build time and also is better for browser caching. (See [Static Asset Handling](static.md))