title: How to get the last key of object which has a value
body: <p>I need to get the last key of an object which has a value. So if this would be the object...</p>
  
  <pre><code>const obj = { first: 'value', second: 'something', third: undefined, fourth: undefined }
  </code></pre>
  
  <p>... I need to get <code>second</code></p>
  
  <pre><code>obj = { first: 'value', second: 'something', third: 'else', fourth: undefined }
  // result should be: 'third'
  obj = { any: 'value', other: 'something', thing: undefined, bla: undefined }
  // result should be: 'other'
  </code></pre>