title: map multiple properties in array of objects to the same array
body: <p>I have an array of objects:</p>
  
  <pre><code>let objArray = [{a: 1, b: 2}, {a: 3, b: 4}, {a: 5, b: 6}]
  </code></pre>
  
  <p>and I want to map the <code>a</code> and <code>b</code> properties to a single array:</p>
  
  <pre><code>[1, 2, 3, 4, 5, 6] //single array with a and b together
  </code></pre>
  
  <p>I could do this:</p>
  
  <pre><code>[...objArray.map(d =&gt; d.a), ...objArray.map(d =&gt; d.b)]
  </code></pre>
  
  <p>However I want to avoid looping through the <code>objArray</code> multiple times.</p>