Date.prototype.getTimezoneOffset()

const date1 = new Date("August 19, 1975 23:15:30 GMT+07:00");
const date2 = new Date("August 19, 1975 23:15:30 GMT-02:00");

console.log(date1.getTimezoneOffset());
// Expected output: your local timezone offset in minutes
// (e.g., -120). NOT the timezone offset of the date object.

console.log(date1.getTimezoneOffset() === date2.getTimezoneOffset());
// Expected output: true

getTimezoneOffset()

var x = new Date();
var currentTimeZoneOffsetInHours = x.getTimezoneOffset() / 60;