title: I can't extend the String prototype in javascript
body: <p>Here is the code</p>
  
  <pre><code>&lt;script&gt;
  
  String.prototype.testthing = function() {
      return "working";
  }
  
  alert(String.testthing());
  
  &lt;/script&gt;
  </code></pre>
  
  <p>When I open this page I get the error below</p>
  
  <pre><code>Uncaught TypeError: Object function String() { [native code] } has no method 'testthing'
  </code></pre>
  
  <p>I cannot figure out why. I've extended the Array prototype with no issues.</p>