title: Unfamiliar variable assignment with parenthesis and commas
body: <p>Why does assigning values with parenthesis like this only evaluate to the last value </p>
  
  <pre><code> var a = (1, 2, 5 - 1); //4
  </code></pre>
  
  <p>It also seems to require the parenthesis</p>
  
  <pre><code>var a = 1, 5 - 1; //SyntaxError: Unexpected number
  </code></pre>