title: Failed to construct 'FormData' error appeared
body: <p>Something wrong is going on with my contact form. Just recently everything was fine but now I can't send the message.
  When I try to submit the form I see this error now:</p>
  
  <blockquote>
    <p>Uncaught TypeError: Failed to construct 'FormData': parameter 1 is not
    of type 'HTMLFormElement'.
        at submitForm (ajax.js:77)
        at HTMLFormElement. (ajax.js:72)
        at HTMLFormElement.dispatch (jquery-3.3.1.js:5183)
        at HTMLFormElement.elemData.handle (jquery-3.3.1.js:4991)</p>
  </blockquote>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>$(document).ready(function() {
  $("#subscribeForm").validator().on("submit", function (event) {
      if (event.isDefaultPrevented()) {
          formError();
          submitMSG(false, "Are you sure you filled form inputs correctly?");
      } else {
          event.preventDefault();
          submitForm();
      }
  });
  function submitForm(){
              var subscribe_email =$("input[name=subscribe_email]").val();
              var formData = new FormData($(this)[0]);
              formData.append('subscribe_email', subscribe_email );
              $.ajax({
                   url: "include/ajax/subscribe.php",
                   type: "POST",
                   contentType: false,
                   processData: false,
                   data: formData,
                   cache: false,
                   success : function(text){
               if (text == "success"){
                   formSuccess();
               } else {
                   formError();
                   submitMSG(false,text);
               }
           }
       });
   }
  function formSuccess(){
      $("#subscribeForm")[0].reset();
      submitMSG("valid", "Your message was successfully sent");
  }
  function formError(){
    submitMSG("invalid", "Something went wrong. Please, try again or contact with our support team.");
  }
  function submitMSG(valid, msg){
      if(valid){
          var msgClasses = "cf-alert alert success";
      } else {
          var msgClasses = "cf-alert alert warning";
      }
      $("#success_submit").removeClass().addClass(msgClasses).text(msg);
  }
  });</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"&gt;&lt;/script&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>What's wrong and why did it suddenly break? Thanks so much in advance, folks.</p>