title: Why javascript `arr.filter(() => true)` removes empty holes?
body: <p>Please see below code, array filter explicitly return <code>true</code> can remove array holes, why is this happening?</p>
  
  <pre class="lang-js prettyprint-override"><code>const array = [0, null, '', undefined, , ,];
  
  console.log(array);
  // =&gt; [0, null, "", undefined, empty × 2]
  
  array.filter(() =&gt; true);
  // =&gt; [0, null, "", undefined]
  </code></pre>