title: Merge two objects in javascript ignoring undefined values
body: <p>I have to merge two objects but I don't want to assign undefined value to defined values.</p>
  <pre><code>A = { activity: 'purchased', count: undefined, time: '09:05:33' }
  B = { activity: 'purchased', count: '51', time: undefined }
  </code></pre>
  <p>When I try Object.assign, undefined is replacing fields that have values.</p>
  <p>What I want</p>
  <pre><code>C = { activity: 'purchased', count: '51', time: '09:05:33' }
  </code></pre>