title: How to append extension in metro.config.js for Metro Bundler?
body: <p>I'm trying to bundle <code>markdown</code> files without creating much overhead (i.e. not adding them manually to the asset bundles in Xcode and Android Studio, not using 3rd party dependencies).</p>
  
  <p>My idea was to allow <code>require()</code> to include them by adjusting the metro bundler settings in <code>metro.config.js</code>:</p>
  
  <pre class="lang-js prettyprint-override"><code>/**
   * Metro configuration for React Native
   * https://github.com/facebook/react-native
   *
   * @format
   */
  
  module.exports = {
      transformer: {
          getTransformOptions: async () =&gt; ({
              transform: {
                  experimentalImportSupport: false,
                  inlineRequires: false,
              },
          }),
      },
      resolver: {
          assetExts: [`md`] // &lt; include md
      }
  };
  </code></pre>
  
  <p>Sadly metro bundler replaces the array of given defaults with what's set here. </p>
  
  <p>I don't want to explicitly repeat the default asset extension list which lists about 20+ file extensions, especially since I want to stick to the defaults otherwise. See: <a href="https://github.com/facebook/metro/blob/master/packages/metro-config/src/defaults/defaults.js" rel="noreferrer">https://github.com/facebook/metro/blob/master/packages/metro-config/src/defaults/defaults.js</a>.</p>
  
  <p>Appending to the array does not work, too.</p>
  
  <p>Using RN 0.59.3.</p>
  
  <p>Anything I'm missing?</p>