title: Get next property of nested object in javascript
body: <p>I have been trying to write a function that would return an another in line property key. </p>
  
  <p>Lets say we have this JSON:</p>
  
  <pre><code>'Test123': {
      'Another Test': {},
      'Test some more': {
          'Still testing?': {
              'Yeah...': {}
          },
          'Never ending story': {}
      }
  },
  </code></pre>
  
  <p>For example, if we pass 'Still testing?' key into the function it should return 'Yeah...', but if we pass 'Yeah...' it should return 'Never ending story'. Doest someone knows who to do it? I have been trying to write a function doing that but my brain doesn't support it...</p>