if ( !window.isValidEmail )
{
    function isValidEmail(email) {
          var regEx = /^[\w\.-]+@[\w-_]+\.([a-z]{2,4}\.)?[a-z]{2,4}$/gi;

          return regEx.test(email);
    }
}
 function clear_emailfield( theEmailField ) 
 {
    if (theEmailField.value == 'Typ hier uw e-mailadres') 
    {
        theEmailField.value = '';
    }
 }
 function fill_emailfield( theEmailField ) 
 {
    if (theEmailField.value == '') 
    {
         theEmailField.value = 'Typ hier uw e-mailadres';
    }
 }
 function handleNewsletterSubscriber() {
	if (!isValidEmail( document.getElementById('email_newsletter').value )) {
		alert('U moet een geldig e-mailadres invullen');
		var theEmailField = document.forms[0].email_newsletter;
		clear_emailfield( theEmailField );
		theEmailField.focus();
	}
	else {
		document.forms[0].cmd.value='subscribe_newsletter';
		document.forms[0].submit();
	}
 }
    
function KeyCheck(e)
{ 
   var KeyID = (window.event) ? event.keyCode : e.keyCode;

   switch(KeyID)
   {
        case 13:
            handleNewsletterSubscriber();
         
            return false;
            break;
   }
}