ReCaptcha 2.0: enable Submit button on callback if recaptcha successful

i did the same thing on my test site. however, i used a button instead of submit, so here:

you must add the property data-callback="enableBtn" data-callback property executes the function specified after accomplishment of recaptcha.

<div class="g-recaptcha" data-sitekey="############-#####" data-callback="enableBtn"></div>

and set the id of the button to whatever id you want to and set it to disabled:

<input type="button" value="Submit" id="button1" disabled="disabled">

then on javascript make a function to enable the button

 function enableBtn(){
   document.getElementById("button1").disabled = false;
 }