use googles new reCaptcha as button +jquery

got some idea, i wrote som contact-formular and want to use the "sucessfull" response as submit-button.

I got that idea to check if this statement becomes true:

if (grecaptcha.getResponse() != "") { }

I just have no idea how? Is there a way to check this statement every second? Would be nice :)

Also tryed some other methods for checking but noting seems to work correctly.

Some help would be nice ;-)