title: How to extend rollup.config.js in Ionic2 app?
body: <p>Here is my solution, but it might not be the proper way:</p>
  
  <p>Create a <code>rollup.config.js</code> file under your app root folder.
  In <code>package.json</code> file, add the following code: </p>
  
  <pre><code>"config": 
  {
  "ionic_rollup": "./rollup.config.js" 
  }
  </code></pre>
  
  <p>In the <code>rollup.config.js</code>, import the existing Ionic rollup config:</p>
  
  <pre><code>var rollupConfig = require('./node_modules/@ionic/app-scripts/config/rollup.config.js');
  
  // Extend your config here.
  
  module.exports = rollupConfig;
  </code></pre>