form_extensions.js

HTMLFormElement.prototype.submitViaXHR = function(success, error) {
  if (this.classList.contains("submitting")) return;

  var xhr         = new XMLHttpRequest(),
      form        = this,
      readyStates = ["unsent", "opened", "headers-received", "loading", "done"];

  form.classList.add("submitting");
  form.classList.remove("errored");
  form.removeAttribute("data-ready-state");

  xhr.addEventListener("readystatechange", function() {
    form.setAttribute("data-ready-state", readyStates[xhr.readyState]);
    if (xhr.readyState == 4) {
      form.classList.remove("submitting");

      switch (xhr.status) {
        case 200:
          success(xhr);
          break;
        default:
          form.classList.add("errored");
          error(xhr);
      }
    }
  });

  xhr.open(form.getAttribute("method"), form.getAttribute("action"));
  xhr.send(new FormData(form));
};