title: Javascript filter but return keys rather than values
body: <p>This function works fine but I don't want it to return the values, but the keys:</p>
  
  <pre><code>const search = [2342,1900,1800,2310]
  
  search = search.filter(function (el) { return el &gt; 2200; });
  </code></pre>
  
  <p>So it should return <code>[0,3]</code> rather than <code>[2342,2310]</code></p>