Webpack rails configs

assets.rake

# lib/tasks/assets.rake
# The webpack task must run before assets:environment task.
# Otherwise Sprockets cannot find the files that webpack produces.
Rake::Task["assets:precompile"]
  .clear_prerequisites
  .enhance(["assets:compile_environment"])

namespace :assets do
  # In this task, set prerequisites for the assets:precompile task
  task compile_environment: :webpack do
    Rake::Task["assets:environment"].invoke
  end

  desc "Compile assets with webpack"
  task :webpack do
    sh "$(npm bin)/webpack --config webpack.rails.config.js"

    path = "app/assets/javascripts/generated/"
    FileUtils.copy_file(Pathname.glob(path+'0.*.rails-bundle.js').first,
                        File.join(path, 'rails-bundle.js'))
  end
end

webpack.common.config.js

const path = require('path');
const webpack = require('webpack');

var config = module.exports = {
    context: __dirname,
    entry: [
        './app/assets/javascripts/MathCrunchApp'
    ]
};

config.resolve = {
    extensions: ['', '.json', '.js']
};

config.loaders = [
    {include: /\.json$/, loaders: ['json-loader']}
];

config.externals = {};

[['jquery', 'jQuery'],
 ['jquery', '$'],
 ['lodash', '_'],
 ['backbone', 'Backbone'],
 ['handlebars', 'Handlebars'],
 ['string', 'string']
].forEach(function (lib) {
    if (!lib) return;

    var name = lib[0],
        variable = lib[1];

    config.loaders.push(
        {test: require.resolve(name), loader: 'expose?'+variable}
    );
    config.externals[name] = 'var '+variable;
});

webpack.rails.config.js

const config = require('./webpack.common.config');

config.output = {
    filename: in_dev() 
        ? 'rails-bundle.js'
        : '[id].[chunkhash].rails-bundle.js',
    path: 'app/assets/javascripts/generated',
    publicPath: getCDN()+'/assets/generated/'
};

config.loaders.push(
    {test: /\.js$/, exclude: /node_modules/, loader: 'babel-loader'}
);

module.exports = config;

function getCDN() {
    var CDNs = {
        staging: '<staging-id>.cloudfront.net',
        production: '<production-id>.cloudfront.net',
        preproduction: '<preproduction-id>.cloudfront.net'
    };

    if (!in_dev()) {
        return "//"+CDNs[process.env.RAILS_ENV.toLowerCase()];
    }
    
    return "";
};

function in_dev() {
    return !process.env.RAILS_ENV || process.env.RAILS_ENV == 'development';
}


// Heroku specific
const devBuild = (typeof process.env.BUILDPACK_URL) === 'undefined';
if (devBuild) {
  console.log('Webpack dev build for Rails'); // eslint-disable-line no-console
  module.exports.devtool = 'eval-source-map';
} else {
  console.log('Webpack production build for Rails'); // eslint-disable-line no-console
}