title: Sum values of a specific property in javascript object
body: <p>On a click event in my application I am returned <code>highlights</code> - an array of features (each time of differing length). So <code>console.log(highlights)</code> produces:</p>
  
  <p><a href="https://i.stack.imgur.com/LdmUEm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/LdmUEm.png" alt="enter image description here"></a> </p>
  
  <p>My objective is to return the sum of the values contained in <code>properties.census2010_Pop2010</code> for each feature in the object.  So far I have tried the code below but nothing is returned in the console.  Any suggestions would be appreciated. </p>
  
  <pre><code>total = Object.create(null);
  
  highlights.feature.properties.forEach(function (a) {
      a.census2010_Pop2010.forEach(function (b) {
          total = total + b.census2010_Pop2010;
      });
  });
  
  console.log(total);
  </code></pre>