How do you get a Captcha Validation error with Google ReCaptcha?

How to prevent form from submission if user has not gone through Google ReCapcha ?

jQuery(document).ready(function(j){
  jQ('#formid').submit(function(e) {
     var recaptcha = j("#g-recaptcha-response").val();
     if ( recaptcha === "" ) {
        e.preventDefault();
        alert("Please check the recaptcha");
     }
  });
});