var isEmail=function(str){
  if (/^\w+([\.-]?\w+)*@\w+([\.-]?\w+)*(\.\w{2,3})+$/.test(str)) return true;
  return false;
}
function emailcheck(form){
  if(isEmail(form.email.value)) return true;
  alert('Invalid email address format.');
  form.email.focus();
  return false;
}
function multiemailcheck(form){
	var arr = form.email.value.split(";");
	var len = arr.length;
	for(var i=0; i<len; i++) {
		if(arr[i].length <= 0)
			continue;
		else
			if(!isEmail(arr[i])) {
				alert('Invalid email: ' + arr[i]);
				return false;
			}
	}
	return true;
}