title: jQuery addClass() with Bootstrap
body: <p>I'm using Bootstrap to develop my php platform.</p>
  
  <p>When i try to use this javascript snippet</p>
  
  <pre><code>if(result == "OK"){
      // If the result is OK applies some effects
      $("#signup" + item).removeClass("error");
      $("#signup" + item).addClass("success");
  } else {
      // Applies some effects and shows the error
      $("#signup" + item).removeClass("success");
      $("#signup" + item).addClass("error");
  }
  </code></pre>
  
  <p>with this html code</p>
  
  <pre><code>&lt;input class="xlarge" id="signupUsername" name="signupUsername" size="30" type="text"&gt;
  </code></pre>
  
  <p>Nothing happens. The "error" or "success" effects are not applied.</p>