Convert script from jQuery to Vanilla JavaScript

  $(document).ready(function() {
    $('.myForm').submit(function (event) {
      var data = $(this);
      $.ajax({
        type: data.attr('method'),
        url: data.attr('action'),
        data: data.serialize(),
        success: function (data) {
          $('.output').html(data);
          $('.myForm input:NOT([type=submit])').val('');
        }
      });
      event.preventDefault();
    });
  });