Javascript Validation for email

function validate(form_id,email) {
 
   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
   var address = document.forms[form_id].elements[email].value;
   if(reg.test(address) == false) {
 
      alert('Invalid Email Address');
      return false;
   }
}

<form id="form_id" method="post" action="action.php" onsubmit="javascript:return validate('form_id','email');">
 
   <input type="text" id="email" name="email" />
 
   <input type="submit" value="Submit" />
</form>

from:　http://www.white-hat-web-design.co.uk/blog/javascript-validation/