title: using underscore's “difference” method on arrays of objects
body: <pre><code>_.difference([], [])
  </code></pre>
  
  <p>this method works fine when i'm having primitive type data like </p>
  
  <pre><code>var a = [1,2,3,4];
  var b = [2,5,6];
  </code></pre>
  
  <p>and the <code>_.difference(a,b)</code> call returns <code>[1,3,4]</code></p>
  
  <p>but in case i'm using object like </p>
  
  <pre><code>var a = [{'id':1, 'value':10}, {'id':2, 'value':20}];
  var b = [{'id':1, 'value':10}, {'id':4, 'value':40}];
  </code></pre>
  
  <p>doesn't seem to work</p>