Check Email format using Javascript

function validatemail()
{

var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
var address = document.form1.txtaltermail.value;
if(reg.test(address) == false)
{
return false;
}
else
{
return(true);
}
}