title: Convert javascript object camelCase keys to underscore_case
body: <p>I want to be able to pass any javascript object containing camelCase keys through a method and return an object with underscore_case keys, mapped to the same values.</p>
  
  <p>So, I have this:</p>
  
  <pre><code>var camelCased = {firstName: 'Jon', lastName: 'Smith'}
  </code></pre>
  
  <p>And I want a method to output this:</p>
  
  <pre><code>{first_name: 'Jon', last_name: 'Jon'}
  </code></pre>
  
  <p>What's the fastest way to write a method that takes any object with any number of key/value pairs and outputs the underscore_cased version of that object? </p>