title: Reverse order of Underscore's `extend` when used in a chain
body: <p>Consider:</p>
  
  <pre><code>var result = _.chain(foo)
    .stuff()
    .morestuff()
    .extend(extraKeysValues)    // &lt;-- problem is here
    .value();
  </code></pre>
  
  <p>What this does is extend the chained data set, with the stuff in <code>extraKeysValues</code>. This can overwrite data.</p>
  
  <p>When used in a <code>chain</code>, I want the opposite behavior - I want to add the chain data to <code>extraKeysValues</code>, so I don't overwrite any data.</p>
  
  <p>So how can I effectively revese the order of <a href="http://underscorejs.org/#extend" rel="nofollow"><code>_.extend(destination, *sources)</code></a> when using inside a chain? I realise it would be a multi-step process, but I don't want to break the chain.</p>