How to detect if a re-Captcha site key is valid via javascript?

Question

I'm attempting to detect the 'Invalid site key' error for googles re-Captcha via javascript so the error can be reported to the server for further handling. I'm using the explicit rendering mode and calling the api function grecaptcha.render('iframeid', {'site-key':'xxx'});although this function doesn't return any error response or throw an exception even if it loads the following:

I can't simply read the loaded error text either as it's loaded in an iframe on a different domain. Is there anyway to detect an invalid site key automatically, either via javascript or server side?

Edit Final solution was to load a test page with phantomjs and parse the html of the recaptcha

Answer 1

Google does not provide methods to verify site key, neither you can hack/access reCaptcha html code by JS since the reCapthca is in an iframe and frame's code is not programmatically accessible client-side.

Its a common mistake to forget to update the allowable domains in the dashboard when pushing a new site live.

Since you manage multiple domains I'd recommend you to use one site key for all of the domains you use. Use secure token for that.

Hack

Another option might be that you develop a script that will visit site(s) of interest, make screenshot/snap of loaded reCaptcha, apply OCR (eg. using this) and return a result if site key is valid or not.