Prototype toggleClassName() Method

Syntax:

element.toggleClassName( className );

Return Value:

Returns an HTML element.

Example:

<html>
<head>
<title>Prototype examples</title>

<script type="text/javascript" 
   src="/javascript/prototype.js">
</script>
<script>

function showResult(){
   if( !$('mutsu').hasClassName('fruit') ){
      // This will return false
      alert( "Class name is not set" );
   }

   $('mutsu').toggleClassName('fruit');
   // This will toggle the class presence

   if( $('mutsu').hasClassName('fruit') ){
      // This returns true
      alert( "Now Class name is set" );
   }
}
</script>
</head>

<body>

  <p>Click the button to see the result.</p>

  <div id="mutsu" class="apple">
     <p>This is test division.</p>
  </div>

  <br />
  <input type="button" value="showResult" 
                          onclick="showResult();"/>

</body>
</html>

To understand it in better way you can Try it yourself.