How to make users re-type email address on register/cart to confirm correct email?

Is there a good method in the templates to require users to re-type their email address for confirmation when registering (register.php) and when checking out (cart.php)? For example, WHMCS has a nice way of confirming the password is correct by re-typing it, but how do I do the same thing on email address to make sure users type correct email address?

add a input field and use javascript to do the validation

seems can't do it on php....tried to add some coding in register.php but it give me error message.

My 2 cents.

Let them register via API from your 100% custom page. This is an example of the result that you can obtain with this approach.

Thanks for your comments. I like the API idea but it creates some other problems in the way I have things setup.

The Javascript idea is great and I used the info here: http://stackoverflow.com/questions/18223467/email-match-with-confirm-email-address-in-contact-form

However, the problem with that code, is the user gets an error message but once they click "ok" on the message, they are allowed to continue without editing and correcting their mistake. What do you suggest I add to the Javascript to ensure both email addresses must match before going through with the form?

It does appear that php would be the best way to validate the form though. What kind of error did you have when you tried php?

This is a tricky question.

Yes, you should validate fields with PHP (server side). In fact if you just use javascript to validate them, users can still skip all your checks by simply disabling javascript on their browsers. So the rule is: server side validation plus (optional) javascript one so that it looks better and works without refreshing any page.

You could validate fields with PHP with this hook point but only when an user has been already registered. If you find that there's something wrong you could probably close his account so that he can't do anything and redirect him to Modify Details page where he needs to update his personal details according to your rules. This server side validation is trigged only if users have turned off javascript.

Anyway again in my opinion the best approach is API since you can't a clean job only editing .tpl file.

This is a tricky question.

....

Anyway again in my opinion the best approach is API since you can't a clean job only editing .tpl file.

Yes I agree. I looked at your fantastic API creation page and I see API is a good idea. However, I need to also include this on the cart.php. The register.php seems easy and straightforward, but messing with cart (and I have multiple languages) seems like a painful experience since there seems so many items to worry about, such as discount codes, payment gateways, etc.

Well you can "inject" your custom registration form even in cart.php. I'm not saying that it's the simplest thing but it's possible and you can finally get rid of standard and limited forms of WHMCS.