The following is a very nice solution to remove all trailing white spaces in a String, it uses the prototype functionality to add a method trimTrailing to the String class:

  <script type="text/javascript">

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

  </script>

You can use this new function in the following way:

  <script type="text/javascript">

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

  </script>