Reverse Captcha Basic

reverse-captcha-basic.html

<!--A basic Reverse Captcha contact form-->
<form id="formAntiSpam" action="" method="">
  <input type="text" name="nome" value="" tabindex="1">
  <input type="text" name="email" value="" tabindex="2">
  
  <!--The spambot test field is hidden and no has a tabindex-->
  <input type="button" class="spam-test-field" style="display:none" value="">
  
  <button type="button" onclick="spamVerify()" tabindex="3"> Send Form </button>
</form>

<script type="text/javascript">
  function spamVerify(evt) {
    // get the spambot test field value
    var getString = document.querySelector(".spam-test-field").value;
    // the test if the field is empty and submit form
    if (getString == "") {
      document.getElementById("formAntiSpam").submit();
    // if not, sending blocks
    } else {
      evt.preventDefault();
    }
  }
</script>