How to mock the browser's timezone? [duplicate]

Question

I want to test a location feature in a web site, to make this test I need to try different time-zones. I obtain the timezone with a javascript code, calling the following function:

var offset = new Date().getTimezoneOffset();

Now this function returns to me 180 because I am in Argentina, I need to test with different time-zones. Somebody knows how to do this? Many thanks!!

Answer 1

The accepted answer doesn't really mock the Date.getTimezoneOffset method, instead it expects you to use a different method with the same name.

It won't work on Date objects themselves and as Carl Meyer points out, it won't work for libraries like MomentJS.

A better way is to override the getTimezoneOffset method on the Date prototype, so that all instances of Date have the overridden method.

d = new Date(); // Mon Jul 13 2015 10:58:12 GMT+0200 (CEST)
alert(d.getTimezoneOffset()); // -120, My local "real" timezone.

// Save the original method.
var getTimezoneOffset = Date.prototype.getTimezoneOffset;

Date.prototype.getTimezoneOffset = function () {
    return 160;
}
// Now Date objects will have the mocked timezone offset
alert(d.getTimezoneOffset()); // 160, The mocked timezone.

// Now restore the method to its original version
Date.prototype.getTimezoneOffset = getTimezoneOffset;
alert(d.getTimezoneOffset()); // -120