Validate Email using JavaScript

You can validate email address while user entering email address in textbox.

if (document.getElementById("<%=txtEmail.ClientID %>").value == "") {
alert("Please Enter Email");
document.getElementById("<%=txtEmail.ClientID %>").focus();
return false;
}
var emailPat = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;
var emailid = document.getElementById("<%=txtEmail.ClientID %>").value;
var matchArray = emailid.match(emailPat);
if (matchArray == null) {
alert("Your Email Address is not valid");
document.getElementById("<%=txtEmail.ClientID %>").focus();
return false;
}