title: Calling reduce to sum array of objects returns NaN
body: <p>I have code similar to this:</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var temp = [ { "y": 32 }, { "y": 60 }, { "y": 60 } ];
  var reduced = temp.reduce(function(a, b) {
    return a.y + b.y;
  });
  
  console.log(reduced); // Prints NaN</code></pre>
  </div>
  </div>
  </p>
  <p>Why does it print <code>NaN</code> instead of <code>152</code>?</p>