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assets-webpack-plugin

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Webpack plugin that emits a json file with assets paths.

Table of Contents

Why Is This Useful?

When working with Webpack you might want to generate your bundles with a generated hash in them (for cache busting).

This plug-in outputs a json file with the paths of the generated assets so you can find them from somewhere else.

Example output:

The output is a JSON object in the form:

{
    "bundle_name": {
        "asset_kind": "/public/path/to/asset"
    }
}

Where:

  • "bundle_name" is the name of the bundle (the key of the entry object in your webpack config, or "main" if your entry is an array).
  • "asset_kind" is the camel-cased file extension of the asset

For example, given the following webpack config:

{
    entry: {
        one: ['src/one.js'],
        two: ['src/two.js']
    },
    output: {
        path: path.join(__dirname, "public", "js"),
        publicPath: "/js/",
        filename: '[name]_[hash].bundle.js'
    }
}

The plugin will output the following json file:

{
    "one": {
        "js": "/js/one_2bb80372ebe8047a68d4.bundle.js"
    },
    "two": {
        "js": "/js/two_2bb80372ebe8047a68d4.bundle.js"
    }
}

Install

npm install assets-webpack-plugin --save-dev

Configuration

In your webpack config include the plug-in. And add it to your config:

var path = require('path')
var AssetsPlugin = require('assets-webpack-plugin')
var assetsPluginInstance = new AssetsPlugin()

module.exports = {
    // ...
    output: {
        path: path.join(__dirname, "public", "js"),
        filename: "[name]-bundle-[hash].js",
        publicPath: "/js/"
    },
    // ....
    plugins: [assetsPluginInstance]
}

Options

You can pass the following options:

filename

Optional. webpack-assets.json by default.

Name for the created json file.

new AssetsPlugin({filename: 'assets.json'})

fullPath

Optional. true by default.

If false the output will not include the full path of the generated file.

new AssetsPlugin({fullPath: false})

e.g.

/public/path/bundle.js vs bundle.js vs

includeManifest

Optional. false by default.

Inserts the manifest javascript as a text property in your assets. Accepts the name of your manifest chunk. A manifest is the last CommonChunk that only contains the webpack bootstrap code. This is useful for production use when you want to inline the manifest in your HTML skeleton for long-term caching. See issue #1315 or a blog post to learn more.

new AssetsPlugin({includeManifest: 'manifest'})
// assets.json:
// {entries: {manifest: {js: `hashed_manifest.js`, text: 'function(modules)...'}}}
//
// Your html template:
// <script>
// {assets.entries.manifest.text}
// </script>

path

Optional. Defaults to the current directory.

Path where to save the created JSON file.

new AssetsPlugin({path: path.join(__dirname, 'app', 'views')})

prettyPrint

Optional. false by default.

Whether to format the JSON output for readability.

new AssetsPlugin({prettyPrint: true})

processOutput

Optional. Defaults is JSON stringify function.

Formats the assets output.

new AssetsPlugin({
  processOutput: function (assets) {
    return 'window.staticMap = ' + JSON.stringify(assets)
  }
})

update

Optional. false by default.

When set to true, the output JSON file will be updated instead of overwritten.

new AssetsPlugin({update: true})

metadata

Inject metadata into the output file. All values will be injected into the key "metadata".

new AssetsPlugin({metadata: {version: 123}})
// Manifest will now contain:
// {
//   metadata: {version: 123}
// }

Using in multi-compiler mode

If you use webpack multi-compiler mode and want your assets written to a single file, you must use the same instance of the plugin in the different configurations.

For example:

var webpack = require('webpack')
var AssetsPlugin = require('assets-webpack-plugin')
var assetsPluginInstance = new AssetsPlugin()

webpack([
  {
    entry: {one: 'src/one.js'},
    output: {path: 'build', filename: 'one-bundle.js'},
    plugins: [assetsPluginInstance]
  },
  {
    entry: {two:'src/two.js'},
    output: {path: 'build', filename: 'two-bundle.js'},
    plugins: [assetsPluginInstance]
  }
])

Using this with Rails

You can use this with Rails to find the bundled Webpack assets via Sprockets. In ApplicationController you might have:

def script_for(bundle)
  path = Rails.root.join('app', 'views', 'webpack-assets.json') # This is the file generated by the plug-in
  file = File.read(path)
  json = JSON.parse(file)
  json[bundle]['js']
end

Then in the actions:

def show
  @script = script_for('clients') # this will retrieve the bundle named 'clients'
end

And finally in the views:

<div id="app">
  <script src="<%= @script %>"></script>
</div>

Test

npm test