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0.9.10 • Public • Published

Sprockets Pre-Loader for Webpack

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Easily translate sprockets require directives into JavaScript module dependencies. Useful for migrating a Rails project to Webpack module bundling.


  • require, require_tree, require_directory, and require_self sprocket directives
  • Vendor assets in vendor/assets/javascripts
  • Gem assets (resulting from bundle show <gem>)
  • JST Eco assets

Using sprockets-preloader


npm install --save sprockets-preloader


Include as a preLoader, e.g.

module: {
  preLoaders: [
    { loader: require.resolve('sprockets-preloader') },

should avoid .erb. and .md files


  • Recommended: webpack-rails gem to integrate webpack asset helpers in Rails
  • Make non_webpack_compatible_before_webpack sprocket asset for all .erb assets
  • Make non_webpack_compatible_after_webpack sprocket asset for all .erb assets dependent on webpack assets
  • Note: any gem's erb dependencies should be included in either of the above files
  • Add coffee-loader to parse CoffeeScript files
  • Add eco-loader to parse Eco files
  • Top-level var expressions actually polluted the global closure. Removing the var keyword should suffice as a transition remedy.

Another configuration example

webpack.config.js should contain something similarly to:

module: {
  preLoaders: [
    { loader: require.resolve('sprockets-preloader') },
  loaders: [
    { test: /\.coffee$/, loader: require.resolve('coffee-loader') },
    { test: /\.eco$/, loader: require.reseolve('eco-loader') },

application.html.erb should contain something similarly to:

  <%= javascript_include_tag 'non_webpack_compatible_before_webpack' %>
  <%= javascript_include_tag *webpack_asset_paths('application') %>
  <%= javascript_include_tag 'non_webpack_compatible_after_webpack' %>

Note: This is not an permanent solution to using JavaScript module dependencies.

Please dedicate time to converting files manually once all dependencies are working with webpack (e.g. development, test, production) Easiest to move gem and vendor dependencies as module dependencies (from NPM or the like). For each JavaScript file in the Rails assets manifest, convert to module dependencies. Perhaps this can be released as a script to convert require directives.

For a more automated approach, consider using another Mavenlink loader: kitno-loader. Although currently in an alpha stage, its goal is to automagically convert (CoffeeScript) files into CommonJS-compliant modules.

As always, once these loaders have reach stability in your codebase, it is encouraged to write to disk.


npm i sprockets-preloader

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