String was not reconized as a valid dateformat

Question

(function ($) {
    $(function () {
        $("#datepicker").datepicker({ dateFormat: 'yy-mm-dd' } );
       $("#timepicker").timepicker({
           timeFormat: 'HH:mm:ss'
       });
       $("#datepickerto").datepicker({ dateFormat: 'yy-mm-dd'  });
       $("#timepickerTo").timepicker({
           timeFormat: 'HH:mm:ss'

       });
    });
})(jQuery);

 targetList = list.getByTitle('AppbokningarList');
    var frDate = new Date(result);
    var tDate = new Date(result2);
    var camlQuery = new SP.CamlQuery(),
        collListItem, strViewXml;

    strViewXml = "<View><Query><OrderBy><FieldRef Name='EventDate'/></OrderBy><Where><And><Lt><FieldRef Name='EndDate'/>";
    strViewXml += "<Value Type='DateTime'>" + frDate.toISOString + "</Value></Lt><Gt><FieldRef Name='EventDate'/>";
    strViewXml += "<Value Type='DateTime'>" + tDate.toISOString + "</Value></Gt></And></Where></Query></View>";

    camlQuery.set_viewXml(strViewXml);
    collListItem = targetList.getItems(camlQuery);
    context.load(collListItem);

UPDATE

var result = listItemCustom + "T" + "" + listItemFromTime + ":00" + ":000" + "Z";
    newItem.set_item('EventDate', result);
    var result2 = listItemtoDate + "T" + "" + listItemToTime + ":00" + ":000" + "Z";
    newItem.set_item('EndDate', result2);

Answer 1

Run into something similar a few days ago. I believe it has to do with the date format. I was using German(Germany) locale (Site Setting > Regional Settings), thus my dates were of format dd.mm.yyyy. When trying to do calculations with the day NaN (not a number) was being returned. I tried the English (United Kingdom) Format, dd/mm/yyyy, which returned a result but wrong value. Finally I tried the English (United States), mm/dd/yyyy which returned the correct results. Apparently JS has trouble recognizing date strings split by '.' and reads them in the US format order (month > date > year). I suggest changing locale in your Regional Settings (Time Zone does not have to Change) and see if you get the correct results. I believe the datejs library helps hundle and calculate in all date formats, but I didn't use it so I can not help you with that. (wanted to post this as a comment, but it seems I don't have enough reputation to do so yet :) )