Проверка различных типов входных данных формы с помощью критериев

document.addEventListener('DOMContentLoaded', function(){
var data = {};

var formToJSON = function formToJSON(form) {
	var data = {};
    for (var i = 0; i < form.length; i++) {
      var item = form[i];


         //looking for checkbox

            if (item.value = = "") {
                continue;
            }
            else {
                if (item.checked == false) {
                    data[item.name] = false;
                }
                else {
                data[item.name] = item.value;
                }
            }
    }
return data; };

  var dataContainer = document.getElementsByClassName('results__display')[0];
  form = document.getElementById('formular').querySelectorAll('input,select,textarea');
  butt = document.getElementById('knopfabsenden');
  butt.addEventListener('click', function (event) {
    event.preventDefault();
      handleFormSubmit(form = form);
  });

  var handleFormSubmit = function handleFormSubmit(event) {
    var data = formToJSON(form);
    dataContainer.textContent = JSON.stringify(data, null, "  ");
    }

}, false);

<div id = "formular">
<label class = "formular__label" for = "machineName">Textfield Test</label>
<input class = "formular__input formular__input--text" id = "machineNumber" name = "machineNumber" type = "text"/>

<br>
<input class = "formular__input formular__input--checkbox" id = "checkTest" name = "checkTest" type = "checkbox" value = "true"/>
<label class = "formular__label formular__label--checkbox" for = "checkTest">Checkbox Test</label>
<br>
<button class = "formular__button" id = "knopfabsenden" type = "submit">Submit</button>
</div>

<div class = "results">
  <h2 class = "results__heading">Form Data</h2>
  <pre class = "results__display-wrapper"><code class = "results__display"></code></pre>
</div>