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Javascript client-side email Validation Script

Here is a client-side email validation example (Updated July 06, 2006):

Put this code in between the <head> and </head> tags:

<SCRIPT LANGUAGE="JavaScript">
   // -->
   function xemailValid (emailStr) {
   var checkTLD=1;
   var knownDomsPat=/^(com|net|org|edu|int|mil|gov|arpa|biz|aero|name|coop|info|pro|museum|tv)$/;
   var emailPat=/^(.+)@(.+)$/;
   var specialChars="\$\$><@,;:\\\\\\\"\\.\\[\\]";
   var validChars="\[^\\s" + specialChars + "\]";
   var quotedUser="(\"[^\"]*\")";
   var ipDomainPat=/^\[(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})\]$/;
   var atom=validChars + '+';
   var word="(" + atom + "|" + quotedUser + ")";
   var userPat=new RegExp("^" + word + "(\\." + word + ")*$");
   var domainPat=new RegExp("^" + atom + "(\\." + atom +")*$");
   var matchArray=emailStr.match(emailPat);
   if (matchArray==null) {
   alert("Email address seems incorrect (check @ and .'s)");
   return false;
   }
   var user=matchArray[1];
   var domain=matchArray[2];
   for (i=0; i<user.length; i++) {
   if (user.charCodeAt(i)>127) {
   alert("Ths username contains invalid characters.");
   return false;
}
}
for (i=0; i<domain.length; i++) {
if (domain.charCodeAt(i)>127) {
alert("Ths domain name contains invalid characters.");
return false;
}
}
if (user.match(userPat)==null) {
alert("The username doesn't seem to be valid.");
return false;
}
var IPArray=domain.match(ipDomainPat);
if (IPArray!=null) {
for (var i=1;i<=4;i++) {
if (IPArray[i]>255) {
alert("Destination IP address is invalid!");
return false;
}
}
return true;
}
var atomPat=new RegExp("^" + atom + "$");
var domArr=domain.split(".");
var len=domArr.length;
for (i=0;i<len;i++) {
if (domArr[i].search(atomPat)==-1) {
alert("The domain name does not seem to be valid.");
return false;
}
}
if (checkTLD && domArr[domArr.length-1].length!=2 && 
domArr[domArr.length-1].search(knownDomsPat)==-1) {
alert("The address must end in a well-known domain or two letter " + "country.");
return false;
}
if (len<2) {
alert("This address is missing a hostname!");
return false;
}
return true;
}
// End -->
</script>

Put this code where you want the email form to sit: