A simple code snippet to disable Sundays and prevent past dates in the Ninja Forms Advanced Datepicker add-on. This solution uses Flatpickr to ensure only future dates can be selected and Sundays are excluded. Perfect for booking forms or scheduling systems where past dates and Sundays aren't valid.

ninja-forms-disable-sundays-and-past-dates-advanced-datepicker.js

/**
 * Ninja Forms - Disable Past Dates and Sundays in Advanced Datepicker
 * @author Faisal Ahammad
 */

jQuery(document).ready(function ($) {
  function initCustomDatePicker() {
    var customDatePicker = Marionette.Object.extend({
      initialize: function () {
        this.listenTo(Backbone.Radio.channel("flatpickr"), "init", this.modifyDatepicker);
      },
      modifyDatepicker: function (dateObject, fieldModel) {
        var currentDate = new Date();
        currentDate.setDate(currentDate.getDate() + 1); // Allow only future dates

        // Disable Sundays
        dateObject.set("disable", [
          function (date) {
            return date.getDay() === 0;
          }
        ]);

        dateObject.set("minDate", currentDate);
      },
    });

    new customDatePicker();
  }

  // Form ID (185) to apply the code on a specific form
  if ($("#nf-form-185-cont").length) {
    initCustomDatePicker();
  } else {
    var observer = new MutationObserver(function (mutations, observerInstance) {
      if ($("#nf-form-185-cont").length) {
        initCustomDatePicker();
        observerInstance.disconnect();
      }
    });

    observer.observe(document.body, { childList: true, subtree: true });
  }
});