html - reCapctcha - form has been validated -

i implementing recaptcha, box checkbox user click , confirm he's not robot being presented, doubt if working, because i'm using if (grecaptcha.getresponse () = = "") , not know if robot circumvent this, because i'm not analyzing response google api returns, i'm checking if there return.

note: page html, implement recaptcha in jsp.

the following code:

function logar(){      if (grecaptcha.getresponse() == "")      {          alert("você não clicou no recaptcha, por favor, faça!")          return false;      } else {          document.login.submit();      }  }

<script src='https://www.google.com/recaptcha/api.js?hl=pt' async defer></script>    <form class="form-inline" role="form" name="login" action="logincontroller.do" method="post">      <div class="modal-body">          usuario: <input type="text" name="login">          senha <input type="text" name="senha">          <div class="g-recaptcha" data-sitekey="xx_chave_xx"></div>      </div>      <div class="modal-footer">          <button type="button" class="btn btn-default" data-dismiss="modal">fechar</button>          <button type="button" class="btn btn-primary" onclick="logar()" >login</button>      </div>  </form>