title: _.each context variable
body: <p>I don't understand the purpose of a context variable for many of the underscore.js functions. What purpose does it serve. I know that it binds "this" in the iterator callback, but I don't understand the practical application of it.</p>
  
  <pre><code>var context = {'a': 'a'};
  _.each([1, 2, 3], function(element, index, list)
  {
      console.log(this);
      console.log(element);
      console.log(index);
      console.log(list);
  }, context);
  </code></pre>