First of all here is the javascript function that tests if an email address is valid.
It checks for a lot of things: to see if the email contains a @ sign and a dot checks to see if the @ is before the dot and so on.
<script>
function isMail(str)
{
var at @ ;
var dot . ;
var lat str.indexOf(at);
var lstr str.length;
var ldot str.indexOf(dot);
if (str.indexOf(at) -1) return false;
if (str.indexOf(at) -1 || str.indexOf(at) 0 || str.indexOf(at) lstr) return false;
if (str.indexOf(dot) -1 || str.indexOf(dot) 0 || str.indexOf(dot) lstr) return false;
if (str.indexOf(at (lat+1))! -1) return false; if (str.substring(lat-1 lat) dot || str.substring(lat+1 lat+2) dot) return false;
if (str.indexOf(dot (lat+2)) -1) return false;
if (str.indexOf( )! -1) return false;
return true;
}
// the next function will be used to validate the form. I made this as a separate function because you might want to validate more fields.
function validate_form()
{
if (!isMail(document.form1.mail.value))
{
alert( Please enter a valid email address );
document.form1.mail.focus();
return false;
}
// if the value entered is not a valid email address
// we show a message focus on the field and return false.
// returning false will make sure the form is not submitted
// if we got here it means the email address is valid
return true;
// return true means that the form is submitted.
}
</script>
After placing this function in the code here is what you need to put in the form.
Let's say the form only has the email address and a submit button.
<form action / method post onsubmit return validate_form() name form1 >
<input type text name email value >
<input type submit name submit_button value continue >
</form>
1 
0