# Using Pre-Processors

In webpack, all pre-processors need to be applied with a corresponding loader. vue-loader allows you to use other webpack loaders to process a part of a Vue component. It will automatically infer the proper loaders to use based on the lang attribute of a language block and the rules in your webpack config.

# Sass

For example, to compile our <style> tag with Sass/SCSS:

npm install -D sass-loader node-sass

In your webpack config:

module.exports = {
  module: {
    rules: [
      // ... other rules omitted

      // this will apply to both plain `.scss` files
      // AND `<style lang="scss">` blocks in `.vue` files
      {
        test: /\.scss$/,
        use: [
          'vue-style-loader',
          'css-loader',
          'sass-loader'
        ]
      }
    ]
  },
  // plugin omitted
}

Now in addition to being able to import 'style.scss', we can use SCSS in Vue components as well:

<style lang="scss">
/* write SCSS here */
</style>

Any content inside the block will be processed by webpack as if it's inside a *.scss file.

# Sass vs SCSS

Note that sass-loader processes the non-indent-based scss syntax by default. In order to use the indent-based sass syntax, you need to pass options to the loader:

// webpack.config.js -> module.rules
{
  test: /\.sass$/,
  use: [
    'vue-style-loader',
    'css-loader',
    {
      loader: 'sass-loader',
      options: {
        indentedSyntax: true,
        // sass-loader version >= 8
        sassOptions: {
          indentedSyntax: true
        }
      }
    }
  ]
}

sass-loader also supports a additionalData option which allows you to share common variables among all processed files without having to explicit import them:

// webpack.config.js -> module.rules
{
  test: /\.scss$/,
  use: [
    'vue-style-loader',
    'css-loader',
    {
      loader: 'sass-loader',
      options: {
        // you can also read from a file, e.g. `variables.scss`
        // use `prependData` here if sass-loader version = 8, or
        // `data` if sass-loader version < 8
        additionalData: `$color: red;`
      }
    }
  ]
}

# LESS

npm install -D less less-loader

// webpack.config.js -> module.rules
{
  test: /\.less$/,
  use: [
    'vue-style-loader',
    'css-loader',
    'less-loader'
  ]
}

# Stylus

npm install -D stylus stylus-loader

// webpack.config.js -> module.rules
{
  test: /\.styl(us)?$/,
  use: [
    'vue-style-loader',
    'css-loader',
    'stylus-loader'
  ]
}

# PostCSS

TIP

Vue Loader v15 no longer applies PostCSS transforms by default. You will need to use PostCSS via postcss-loader.

npm install -D postcss-loader

// webpack.config.js -> module.rules
{
  test: /\.css$/,
  use: [
    'vue-style-loader',
    {
      loader: 'css-loader',
      options: { importLoaders: 1 }
    },
    'postcss-loader'
  ]
}

Configuration of PostCSS can be done via postcss.config.js or postcss-loader options. For details, consult postcss-loader docs.

postcss-loader can also be applied in combination with other pre-processors mentioned above.

# Babel

npm install -D babel-core babel-loader

// webpack.config.js -> module.rules
{
  test: /\.js?$/,
  loader: 'babel-loader'
}

Configuration of Babel can be done via .babelrc or babel-loader options.

# Excluding node_modules

It is common to have exclude: /node_modules/ for JS transpilation rules (e.g. babel-loader) that apply to .js files. Due to the inference change of v15, if you import a Vue SFC inside node_modules, its <script> part will be excluded from transpilation as well.

In order to ensure JS transpilation is applied to Vue SFCs in node_modules, you need to whitelist them by using an exclude function instead:

{
  test: /\.js$/,
  loader: 'babel-loader',
  exclude: file => (
    /node_modules/.test(file) &&
    !/\.vue\.js/.test(file)
  )
}

# TypeScript

npm install -D typescript ts-loader

// webpack.config.js
module.exports = {
  resolve: {
    // Add `.ts` as a resolvable extension.
    extensions: ['.ts', '.js']
  },
  module: {
    rules: [
      // ... other rules omitted
      {
        test: /\.ts$/,
        loader: 'ts-loader',
        options: { appendTsSuffixTo: [/\.vue$/] }
      }
    ]
  },
  // ... plugin omitted
}

Configuration of TypeScript can be done via tsconfig.json. Also see docs for ts-loader.

# Pug

Processing templates is a little different, because most webpack template loaders such as pug-loader return a template function instead of a compiled HTML string. Instead of using pug-loader, we need to use a loader that returns the raw HTML string, e.g. pug-plain-loader:

npm install -D pug pug-plain-loader

// webpack.config.js -> module.rules
{
  test: /\.pug$/,
  loader: 'pug-plain-loader'
}

Then you can write:

<template lang="pug">
div
  h1 Hello world!
</template>

If you also intend to use it to import .pug files as HTML strings in JavaScript, you will need to chain raw-loader after the preprocessing loader. Note however adding raw-loader would break the usage in Vue components, so you need to have two rules, one of them targeting Vue files using a resourceQuery, the other one (fallback) targeting JavaScript imports:

// webpack.config.js -> module.rules
{
  test: /\.pug$/,
  oneOf: [
    // this applies to `<template lang="pug">` in Vue components
    {
      resourceQuery: /^\?vue/,
      use: ['pug-plain-loader']
    },
    // this applies to pug imports inside JavaScript
    {
      use: ['raw-loader', 'pug-plain-loader']
    }
  ]
}