# Working with Webpack

# Simple Configuration

The easiest way to tweak the webpack config is providing an object to the configureWebpack option in svelte.config.js:

// svelte.config.js
module.exports = {
  configureWebpack: {
    plugins: [
      new MyAwesomeWebpackPlugin()
    ]
  }
}

The object will be merged into the final webpack config using webpack-merge.

If you need conditional behavior based on the environment, or want to directly mutate the config, use a function (which will be lazy evaluated after the env variables are set). The function receives the resolved config as the argument. Inside the function, you can either mutate the config directly, OR return an object which will be merged:

// svelte.config.js
module.exports = {
  configureWebpack: config => {
    if (process.env.NODE_ENV === 'production') {
      // mutate config for production...
    } else {
      // mutate for development...
    }
  }
}

# Chaining (Advanced)

The internal webpack config is maintained using webpack-chain. The library provides an abstraction over the raw webpack config, with the ability to define named loader rules and named plugins, and later "tap" into those rules and modify their options.

This allows us finer-grained control over the internal config. Below you will see some examples of common modifications done via the chainWebpack option in svelte.config.js.

# Modifying Options of a Loader

// svelte.config.js
module.exports = {
  chainWebpack: config => {
    config.module
      .rule('vue')
      .use('vue-loader')
        .loader('vue-loader')
        .tap(options => {
          // modify the options...
          return options
        })
  }
}

# Adding a New Loader

// svelte.config.js
module.exports = {
  chainWebpack: config => {
    // GraphQL Loader
    config.module
      .rule('graphql')
      .test(/\.graphql$/)
      .use('graphql-tag/loader')
        .loader('graphql-tag/loader')
        .end()
  }
}

# Replacing Loaders of a Rule

If you want to replace an existing Base Loader, for example using vue-svg-loader to inline SVG files instead of loading the file:

// svelte.config.js
module.exports = {
  chainWebpack: config => {
    const svgRule = config.module.rule('svg')

    // clear all existing loaders.
    // if you don't do this, the loader below will be appended to
    // existing loaders of the rule.
    svgRule.uses.clear()

    // add replacement loader(s)
    svgRule
      .use('vue-svg-loader')
        .loader('vue-svg-loader')
  }
}

# Modifying Options of a Plugin

// svelte.config.js
module.exports = {
  chainWebpack: config => {
    config
      .plugin('html')
      .tap(args => {
        return [/* new args to pass to html-webpack-plugin's constructor */]
      })
  }
}

You will need to familiarize yourself with webpack-chain's API and read some source code in order to understand how to leverage the full power of this option, but it gives you a more expressive and safer way to modify the webpack config than directly mutate values.

For example, say you want to change the default location of index.html from /Users/username/proj/public/index.html to /Users/username/proj/app/templates/index.html. By referencing html-webpack-plugin you can see a list of options you can pass in. To change our template path we can pass in a new template path with the following config:

// svelte.config.js
module.exports = {
  chainWebpack: config => {
    config
      .plugin('html')
      .tap(args => {
        args[0].template = '/Users/username/proj/app/templates/index.html'
        return args
      })
  }
}

You can confirm that this change has taken place by examining the vue webpack config with the vue inspect utility, which we will discuss next.

# Inspecting the Project's Webpack Config

Since @svel/cli-service abstracts away the webpack config, it may be more difficult to understand what is included in the config, especially when you are trying to make tweaks yourself.

vue-cli-service exposes the inspect command for inspecting the resolved webpack config. The global vue binary also provides the inspect command, and it simply proxies to vue-cli-service inspect in your project.

The command will print the resolved webpack config to stdout, which also contains hints on how to access rules and plugins via chaining.

You can redirect the output into a file for easier inspection:

vue inspect > output.js

Note the output is not a valid webpack config file, it's a serialized format only meant for inspection.

You can also inspect a subset of the config by specifying a path:

# only inspect the first rule
vue inspect module.rules.0

Or, target a named rule or plugin:

vue inspect --rule vue
vue inspect --plugin html

Finally, you can list all named rules and plugins:

vue inspect --rules
vue inspect --plugins

# Using Resolved Config as a File

Some external tools may need access to the resolved webpack config as a file, for example IDEs or command line tools that expect a webpack config path. In that case you can use the following path:

<projectRoot>/node_modules/@svel/cli-service/webpack.config.js

This file dynamically resolves and exports the exact same webpack config used in vue-cli-service commands, including those from plugins and even your custom configurations.