Javascript : URL Validation

function urlValidator(elem, helperMsg){
	var urlExp = /^http?\:\/\/(www\d?\d?\d?\d?\.)?([A-Za-z0-9-_]+\.)?[A-Za-z0-9-_]+((\.[A-Za-z]{2,6})(\.[A-Za-z]{2})?([0-9-_%&\?\/\.=]*))$/;
	if(elem.value.match(urlExp)){
		return true;
	} else {
		alert(helperMsg);
		elem.focus();
		return false;
	}
}