Which email detection regex is better?

Question

Here I have 2 email validation regexps, which one is better and why?

new RegExp("^[a-zA-Z0-9_-]+@[a-zA-Z0-9-]{2,}[.][a-zA-Z]{2,}$", "i");

new RegExp("^([a-zA-Z0-9._%-]+@[a-zA-Z0-9.-]+.[a-zA-Z]{2,4})*$", "");

Answer 1

There probably is no 'good' regexp to validate an email id. The Internet Standard RFC has classified a 500-character long RegExp which according to them is the standard way to validate an email-id. Well, it does work, but it is so messy and almost impossible for most of us to understand.

(?:[a-z0-9!#$%&'*+/=?^_`{|}~-]+(?:\.[a-z0-9!#$%&'*+/=?^_`{|}~-]+)*|"(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21\x23-\x5b\x5d-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])*")@(?:(?:[a-z0-9](?:[a-z0-9-]*[a-z0-9])?\.)+[a-z0-9](?:[a-z0-9-]*[a-z0-9])?|\[(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?|[a-z0-9-]*[a-z0-9]:(?:[\x01-\x08\x0b\x0c\x0e-\x1f\x21-\x5a\x53-\x7f]|\\[\x01-\x09\x0b\x0c\x0e-\x7f])+)\])

If you have understood it, then, you need not read further. But if you haven't, go on.

This page gives a decent info on how to validate an email id using regexp.

I use this one

RegExp("^[A-Z0-9._%+-]+@([A-Z0-9.-]+\.){1,4}[A-Z]{2,4}$","i")

This works fine, atleast for me, but it fails to validate emails on .museum domain or any other domain longer than 4-characters.

Coming to your patterns, both of them are almost same except the fact that the first one uses i modifier and it allows 2 or more than 2 characters as TLD. And DON'T accept the '+' character, IT IS NOT VALID!

Hope it helps.

Answer 2

Both are totally broken as they both fail to accept the + character in the local part and one of them requires more than one digit for the domain name. Single-digit domain names are perfectly fine in some TLDs (such as .de).

If you really need more validation than a simple "has the *@*.* format" check, you need to read this answer on Stack Overflow: Using a regular expression to validate an email address