Calculate the UTC offset given a TimeZone string in JavaScript

Question

Using the standard JS library (ECMA5), without using momentjs or external libs, how do you calculate the UTC offset given a TimeZone string such as \"Europe/Rome\"

Answer 1

For others who may land on this question, there is a method available on the standard Date function in JavaScript to get the offset from UTC called getTimezoneOffset.

Usage is simply (for example): new Date().getTimezoneOffset(). This returns the number of minutes the current timezone is from UTC. NOTE: It returns a negative number if the current timezone is ahead of UTC. For example, if the user's timezone is UTC+1, -60 is returned.