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/* app/javascript/packs/application.js */
require("@rails/ujs").start();
require("@rails/activestorage").start();

require("packs/example1");
require("packs/example2");
require("packs/example3");

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/* app/javascript/packs/example2.js */

// to call example1 var, you need:

import example1 from './example1';

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/* app/javascript/packs/example1.js */

var example1 = function doSomething() {
  // Your codes here
}

export default example1;

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/* app/javascript/packs/application.js */
require("@rails/ujs").start();
require("@rails/activestorage").start();

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// config/webpack/production.js
process.env.NODE_ENV = 'production';

const environment = require('./environment');

module.exports = environment.toWebpackConfig();

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// config/webpack/loaders/erb.js
module.exports = {
  test: /\.erb$/,
  enforce: 'pre',
  exclude: /node_modules/,
  use: [{
    loader: 'rails-erb-loader',
    options: {
      runner: (/^win/.test(process.platform) ? 'ruby ' : '') + 'bin/rails runner'
    }

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// config/webpack/loaders/custom_loaders.js
module.exports = {
  test: /\.ya?ml$/,
  loaders: ['json-loader', 'yaml-loader']
};

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gem "webpacker"

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- //= jquery_ujs
+ //= require rails-ujs

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<script src="/assets/jquery.js"></script>
<script src="/assets/jquery_ujs.js"></script>