JavaScript SP.CamlQuery() return DateTime fields with offset (in my case +11 hours)

Question

JavaScript SP.CamlQuery() return DateTime fields with offset (in my case +11 hours). In standart Display/Edit forms and views display correct DateTime.

How to get correct DateTime via SP.CamlQuery()?

UPD: JS to get list items

var caml = new SP.CamlQuery();
caml.set_viewXml(...);

var bookingsItems = this._bookingsList.getItems(caml);
this._context.load(bookingsItems);

this._context.executeQueryAsync(function (sender, args) {
    var enumerator = bookingsItems.getEnumerator();

    var items = [];
    while (enumerator.moveNext()) {
        var listItem = enumerator.get_current();
        var bookingStart = listItem.get_item('BookingStart') // DateTime 
    }
}, this._QuerylogProcess);

For example bookingStart = 2012-8-14 12:00. If open DispForm.aspx for this listItem bookingStart = 2012-8-14 1:00

UPD: Solution with server insert: C# code to calculate web reginal settings offset:

private TimeSpan _GetUtcOffset(SPWeb web)
{
    DateTime utcDate = DateTime.UtcNow;
    DateTime localDate = web.RegionalSettings.TimeZone.UTCToLocalTime(utcDate);
    return localDate - utcDate;
}

JavaScript function to calculate correct dateTime

var dateTimeCalculateConsideringWebRegionalSettings = function(date){
    var utcOffsetMinutes = <%= Convert.ToInt32(UtcOffset.TotalMinutes) %> + new Date().getTimezoneOffset();

    var newDate = new Date(date.getTime());
    newDate.setTime(newDate.getTime() + (utcOffsetMinutes*60*1000));
    return newDate;
}

Use js function:

var bookingStart = dateTimeCalculateConsideringWebRegionalSettings(listItem.get_item('BookingStart'));

Answer 1

Very interesting question.

When you retrieve the datetime field with SharePoint javascript API, you get date object which has everything you need, the date and time and offset. Work with this as with an object.

Here is an example where I get a listitem and a datetime field ("Modified" in my case) I have two hours offset: 11.28 gmt+2h, when I create a iso string it becomes 09.28Z (zero time)

By the way, your question has a little to do with CamlQuery. No need to use CamlQuery in the title.

EDIT: If you want to show the same datetime as it is defined in web regional settings, maybe the best way is that you showed (by calculating the offset spweb + local).