Get Date Time value from datetime field in power portal/ power page using jQuery

If you want to get Date & Time field value and want to compare with current date so that you do not want to allow submitting back dated value then use below code in power portal/power page form.

if (window.jQuery) {
   (function ($) {
      if (typeof (entityFormClientValidate) != 'undefined') {
         var originalValidationFunction = entityFormClientValidate;
         if (originalValidationFunction && typeof (originalValidationFunction) == "function") {
            entityFormClientValidate = function() {
               originalValidationFunction.apply(this, arguments);
               // do your custom validation here
               // return false; // to prevent the form submit you need to return false
               // end custom validation.
                var selectedAppDate = $("#lifeline_appointmentdate").datepicker({ dateFormat: 'yyyy-MM-dd' }).val();;
                selectedAppDate = new Date(selectedAppDate);
                var currentDateNow = new Date();

                alert(selectedAppDate);
                alert(currentDateNow);

                if(selectedAppDate < currentDateNow)
                {
                    alert("backdated appointment date is not allowed.");
                    return false;
                }
                else{
                        return true;
                }       
            };
         }
      }
   }(window.jQuery));
}

Now when user will submit with back dated appointment, then submit button will not work. If future dated supplied than it will work.

Hope it helps.