add or subtract timezone difference to javascript Date

What is the best approach to add or subtract timezone differences to the targetTime variable below. The GMT timezone values开发者_如何学编程 comes from the DB in this format: 1.00 for London time, -8.00 for Pacific time and so on.

Code looks like this:

date = "September 21, 2011 00:00:00";
targetTime = new Date(date);

You can use Date.getTimezoneOffset which returns the local offset from GMT in minutes. Note that it returns the value with the opposite sign you might expect. So GMT-5 is 300 and GMT+1 is -60.

var date = "September 21, 2011 00:00:00";
var targetTime = new Date(date);
var timeZoneFromDB = -7.00; //time zone value from database
//get the timezone offset from local time in minutes
var tzDifference = timeZoneFromDB * 60 + targetTime.getTimezoneOffset();
//convert the offset to milliseconds, add to targetTime, and make a new Date
var offsetTime = new Date(targetTime.getTime() + tzDifference * 60 * 1000);

Simple function that works for me:

adjustForTimezone(date:Date):Date{
    var timeOffsetInMS:number = date.getTimezoneOffset() * 60000;
    date.setTime(date.getTime() + timeOffsetInMS);
    return date
}

If you need to compensate the timezone I would recommend the following snippet:

var dt = new Date('2018-07-05')
dt.setMinutes(dt.getMinutes() + dt.getTimezoneOffset())
console.log(dt)

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/getTimezoneOffset

The getTimezoneOffset() method returns the difference, in minutes, between a date as evaluated in the UTC time zone, and the same date as evaluated in the local time zone.

So all you need is to compensate, IN MINUTES

This example shows how to use the local datetime but format it as ISO:

const d = new Date();

let dtOffset = new Date(d.setMinutes(d.getMinutes() - d.getTimezoneOffset()));
// Date in EST and ISO format: "2021-11-30T15:33:32.222Z"
console.log(dtOffset.toISOString());

Typescript version of @alexp answer

     adjustForTimezone(d:Date, offset:number):Date{
        var date = d.toISOString();
        var targetTime = new Date(date);
        var timeZoneFromDB = offset; //time zone value from database
        //get the timezone offset from local time in minutes
        var tzDifference = timeZoneFromDB * 60 + targetTime.getTimezoneOffset();
        //convert the offset to milliseconds, add to targetTime, and make a new Date
        var offsetTime = new Date(targetTime.getTime() + tzDifference * 60 * 1000);
        return offsetTime;
      }