How to get time zone offset in javascript?

Here is the function:

function getTimeZoneOffset() {
var currentDate = new Date();
var date1 = new Date(currentDate.getFullYear(), 0, 1, 0, 0, 0, 0);
var temp = date1.toGMTString();
var date3 = new Date(temp.substring(0, temp.lastIndexOf(” “)));
var hoursDiffStdTime = ((date1 – date3) / (1000 * 60 * 60)) * 60;
return hoursDiffStdTime;
}

And if you want to get the offset with daylight saving then look at the below function:

function getTimeZoneOffsetDayLightSaving() {
var currentDate = new Date();
var date2 = new Date(currentDate.getFullYear(), 6, 1, 0, 0, 0, 0);
var temp = date2.toGMTString();
var date4 = new Date(temp.substring(0, temp.lastIndexOf(” “)));
var hoursDiffDaylightTime = ((date2 – date4) / (1000 * 60 * 60)) * 60;

return hoursDiffDaylightTime;
}