title: Find the common members of two Javascript objects
body: <p>What is the easiest way to find the common members in two Javascript objects? <strong>This question is not about equality.</strong> I don't care about the values of each member, just that they exist in both objects.</p>
  
  <p>Here's what I've done so far (using underscore.js):</p>
  
  <pre><code>_.intersection(_.keys({ firstName: 'John' }), _.keys({ firstName: 'Jane', lastName: 'Doe' }))
  </code></pre>
  
  <p>This gives me a result of <code>['firstName']</code> as expected, but I would like to find an easier or more efficient way, preferably vanilla Javascript.</p>
  
  <ul>
  <li>Is there a better/easier way to do this with underscore?</li>
  <li>Is there a better/easier way to do this <strong>without</strong> underscore (preferred)?</li>
  </ul>