Check email in html form

<script type="text/javascript">

function check_email(email_id, err_id){
emailRegExp = /^[_a-z0-9-]+(\.[_a-z0-9-]+)*@[a-z0-9]+(\.[a-z0-9]+)*(\.([a-z]){2,4})$/;
var err_mail='Email address incorrect!';
if(emailRegExp.test(document.getElementById(email_id).value)){
alert('true');
return true;
}else{
document.getElementById(err_id).innerHTML=err_mail;
alert(err_mail);
return false;
}
}
</script>



<span id="err_msg" style="color: red;"></span>
<form id="myForm" name="myForm" action="./register.php" method="post" onsubmit="return check_email('email','err_msg');">
<input type="text" name="email" id="email" size="20"/>
<input type="submit" name=send" value="Send" />
</form>