setTimezoneOffset globally for whole script

Question

Hello I am using getTimezoneOffset an it returns e.g. -60

How could I set global timezone offset for javascript? I tried setTimezoneOffset('-120'); but it is not working. I would like to set it globally at start of the script so later I will be able simply call var d = new Date(); var n = d.getTimezoneOffset(); and it returns my value. Please just solution exactly for this case. Thank you!

• Oriol: Use UTC date methods instead of local ones, and subtract the offset when needed.
• Teemu: Basicly Date.prototype.getTimezoneOffset = function () {return -120;}; does what you need (and exactly for your case only), but what's the point, why not use a regular variable?
• Jonathan Lonowski: JavaScript doesn't really have an option built-in for specifying a timezone to use. Dates understand only 2 -- UTC/GMT and "local." And, the latter is determined by the user's system.
• peter: Thank you guys! Especially Teemu - it works! :) Sometimes I need to have the same TimezoneOffset for all users.

Answer 1

Date.prototype.getTimezoneOffset = function () {return -120;};

• P Varga: new Date instances don't seem to take this into account though
• Maxmaxmaximus: Date.prototype.getTimezoneOffset = function () {return -520}; hours1 = new Date().getHours(); Date.prototype.getTimezoneOffset = function () {return -120}; hours2 = new Date().getHours(); hours1 === hours2 // true

Answer 2

Using:

// TO ALL dates
Date.timezoneOffset(-240) // +4 UTC
// Override offset only for THIS date
new Date().timezoneOffset(-180) // +3 UTC

Code:

Date.prototype.timezoneOffset = new Date().getTimezoneOffset();
Date.setTimezoneOffset = function(timezoneOffset) {
 return this.prototype.timezoneOffset = timezoneOffset;
};
Date.getTimezoneOffset = function(timezoneOffset) {
 return this.prototype.timezoneOffset;
};
Date.prototype.setTimezoneOffset = function(timezoneOffset) {
 return this.timezoneOffset = timezoneOffset;
};
Date.prototype.getTimezoneOffset = function() {
 return this.timezoneOffset;
};
Date.prototype.toString = function() {
 var offsetDate, offsetTime;
 offsetTime = this.timezoneOffset * 60 * 1000;
 offsetDate = new Date(this.getTime() - offsetTime);
 return offsetDate.toUTCString();
};
['Milliseconds', 'Seconds', 'Minutes', 'Hours', 'Date', 'Month', 'FullYear', 'Year', 'Day'].forEach((function(_this) {
 return function(key) {
 Date.prototype["get" + key] = function() {
 var offsetDate, offsetTime;
 offsetTime = this.timezoneOffset * 60 * 1000;
 offsetDate = new Date(this.getTime() - offsetTime);
 return offsetDate["getUTC" + key]();
 };
 return Date.prototype["set" + key] = function(value) {
 var offsetDate, offsetTime, time;
 offsetTime = this.timezoneOffset * 60 * 1000;
 offsetDate = new Date(this.getTime() - offsetTime);
 offsetDate["setUTC" + key](value);
 time = offsetDate.getTime() + offsetTime;
 this.setTime(time);
 return time;
 };
 };
})(this));

Coffee version:

Date.prototype.timezoneOffset = new Date().getTimezoneOffset()
Date.setTimezoneOffset = (timezoneOffset)->
 return @prototype.timezoneOffset = timezoneOffset
Date.getTimezoneOffset = (timezoneOffset)->
 return @prototype.timezoneOffset
Date.prototype.setTimezoneOffset = (timezoneOffset)->
 return @timezoneOffset = timezoneOffset
Date.prototype.getTimezoneOffset = ->
 return @timezoneOffset
Date.prototype.toString = ->
 offsetTime = @timezoneOffset * 60 * 1000
 offsetDate = new Date(@getTime() - offsetTime)
 return offsetDate.toUTCString()
[
 'Milliseconds', 'Seconds', 'Minutes', 'Hours',
 'Date', 'Month', 'FullYear', 'Year', 'Day'
]
.forEach (key)=>
 Date.prototype["get#{key}"] = ->
 offsetTime = @timezoneOffset * 60 * 1000
 offsetDate = new Date(@getTime() - offsetTime)
 return offsetDate["getUTC#{key}"]()
 Date.prototype["set#{key}"] = (value)->
 offsetTime = @timezoneOffset * 60 * 1000
 offsetDate = new Date(@getTime() - offsetTime)
 offsetDate["setUTC#{key}"](value)
 time = offsetDate.getTime() + offsetTime
 @setTime(time)
 return time