The following is a very nice solution to perform a trim() function on a String, it uses the prototype functionality to add a method trim to the String class:

  <script type="text/javascript">

    String.prototype.trim=trim;
 
    function trim() {               
      return this.replace(/^\s+|\s+$/g,'');
    }

  </script>

You can use this new function in the following way:

  <script type="text/javascript">

    var text = "  HELLO  ";
    alert(text.trim());

  </script>