SharePoint 2013. Update list item dateTime field via JavaScript Client Object Model

SharePoint Client Object Model expects the dates to be in UTC. Example below show how to update list item dateTime field via JavaScript Client Object Model using the SP.TimeZone.localTimeToUTC method.

function addBrowserUtcOffset(date) {
    var utcOffsetMinutes = date.getTimezoneOffset();
    var newDate = new Date(date.getTime());
    newDate.setTime(newDate.getTime() - (utcOffsetMinutes*60*1000));

    return newDate;
}


function updateListItem() {
    this.clientContext = new SP.ClientContext();
    var date = new Date(2012, 8, 17, 5, 0);
    console.log(date);
    this.isoDate = clientContext.get_web().get_regionalSettings().get_timeZone().localTimeToUTC(date.toISOString());

    clientContext.executeQueryAsync(
        Function.createDelegate(this, this.onGetDate),
        Function.createDelegate(this, this.onQueryFailed)
    );
}

function onGetDate() {
    var dateToInsert = addBrowserUtcOffset(this.isoDate.get_value());

    var oList = this.clientContext.get_web().get_lists().getByTitle('testlist');
    var oListItem = oList.getItemById(1);
    oListItem.set_item('dateField', dateToInsert.toISOString());
    oListItem.update();

    this.clientContext.executeQueryAsync(
        Function.createDelegate(this, this.onUpdate),
        Function.createDelegate(this, this.onQueryFailed)
    );
}

function onUpdate() {
    console.log('DONE');
}

function onQueryFailed(sender, args) {
    console.log('Request failed. ' + args.get_message() + '\n' + args.get_stackTrace());
}

updateListItem();