Hubspot Form validation function

hubspotValidate.js

hbspt.forms.create({
  portalId: 'PORTAL_ID',
  formId: 'FORM_ID',
  onFormReady: function($form) {
    var $formRequiredElements = $form.find('[required]');

    var formRequiredFields = [];

    $formRequiredElements.each(function() {
      var fieldName = $(this).attr('name');

      if (!fieldName) {
        fieldName = $(this)
          .find('[name]')
          .attr('name');
      }

      formRequiredFields.push(fieldName);
    });

    function validateForm() {
      var fields = $(this).serializeArray();

      var isValid = true;

      formRequiredFields.forEach(function(fieldName) {
        var field = fields.filter(function(field) {
          return field.name === fieldName;
        })[0];

        if (!field || field.value === undefined || field.value === '') {
          isValid = false;
        }
      });

      $form.find('input[type="submit"]').prop('disabled', !isValid);
    }

    validateForm();

    $form.on('change, input', validateForm);
  }
});