What is the best way to handle time zones with Javascript

Question

I have an authenticated user with a given time zone, e.g. "Berlin, GMT+1". For the sake of this question let's say I have this in the global scope:

var timeZone = "Berlin";
var gmtDistance = 1;

What is the best solution to have all the date-related JS to behave accordingly, meaning that if I create a new Date object it will take the timezone into account.

---

I thought it'd be pretty straightforward, but I don't seem to find the perfect way to do this on Google/SO. I would privilege an answer that doesn't need any external library.

Answer 1

My preference is to store all dates on the server side using UTC time, and when I am handling data coming back via AJAX calls, to create a global handler which does some parsing.

The following example allows you to simply use:

app.ajax({
    url: '/My/Post/Url',
    data: {
        MyProperty: 'MyValue'
    },
    success: function (data, status, xhr) {
        // Do stuff here...
    },
    error: function (xhr, settings, error) {
        // Do stuff here...
    }
});

But, it pre-parses any returned values in the "success" function's "data" element by fixing dates for UTC time to the local timezone. Be aware - after doing this, if you further process the data, you will need to UN-fix it before sending back to the server, or you'll be posting it back up with the offset.

var app = window.app = $.extend(true, {}, app, {
    // Creating a namespace for my app which is safe across multiple files.
    ajax: function (options) {
        var defaultSettings = {
            type: 'POST',
            async: true
        };

        // Capture the settings.
        var settings = $.extend(true, {}, defaultSettings, options);

        // Install our general handlers;
        if (settings.success) {
            settings.success = function (data, textStatus, jqXHR) {
                app.OnPostSuccess(data, textStatus, jqXHR, options.success);
            }
        } else 
            settings.success = app.OnPostSuccess;

        if (settings.error) {
            settings.error = function (jqXHR, ajaxSettings, thrownError) {
                app.OnPostError(event, jqXHR, ajaxSettings, thrownError, options.error);
            }
        } else
            settings.error = app.OnPostError;

        $.ajax(settings);
    },
    OnPostSuccess: function (data, textStatus, jqXHR, fn_after) {
        // Do my generalized success handling here.

        // Fix Dates.
        var fixedData = app.FixDate(data);

        // Call any other handler that's been specified.
        if (typeof fn_after === 'function')
            fn_after(fixedData, textStatus, jqXHR);
    },
    OnPostError: function (jqXHR, ajaxSettings, thrownError, fn_after) {
        // Do my generalized error handling here.

        // Call any other handler that's been specified.
        if (typeof fn_after === 'function')
            fn_after(jqXHR, ajaxSettings, thrownError);
    },
    FixDate: function (obj) {
        var fixed = obj;

        if (typeof obj == 'string' && obj.indexOf('\/Date(') == 0) {
            // Microsoft date "/Date(12345678)/" - convert to real date.
            fixed = new Date(parseInt(fixed.substr(6, fixed.length - 8), 10));
        }

        if (typeof fixed === 'object') {
            if (fixed.getTimezoneOffset) {
                // If the value is a date, apply timezone correction.
                var now = new Date();
                var offset = now.getTimezoneOffset(); // # of minutes from GMT.
                fixed = new Date(fixed.getTime() + offset * 60000);
                // This updates the value based on the offset.
            } else {
                // Otherwise, update each of its properties.
                // This fixes objects with dates for properties, recursively.
                $.each(fixed, function (index, value) {
                    fixed[index] = app.FixDate(value);
                });
            }
        }

        return fixed;
    }
});

All of that set-up to get to this. If you now handle things like dates within OnPostSuccess, you can ensure that they are always in the right format - and always in the right timezone.

Whether or not you use the above AJAX methods, you can use the FixDate method as follows:

var MyObj = { 
    MyDate: "\/Date(12345678)\/"
};

console.log('Before: ', MyObj.MyDate);
MyObj = app.FixDate(MyObj);
console.log('After: ', MyObj.MyDate);

To see the example in action, check out the following jsFiddle:

http://jsfiddle.net/TroyAlford/TBNVV/

Note: this also includes the AJAX bits - but they aren't used in the example - only there for completeness.