HKT (GMT +8) to GMT

var d = new Date();

d.setTime(eventTimestamp);

d.setHours(9);

d.setMinutes(9);

var milliseconds = (d.getMilliseconds() < 10 ? '00' : (d.getMilliseconds() < 100 ? '0' : '')) + d.getMilliseconds();

TimeStamp_old = ("" + d.getFullYear() + (d.getMonth() < 9 ? '0' : '') + (d.getMonth() + 1) + (d.getDate() < 9 ? '0' : '') + d.getDate() + 'T' + (d.getHours() < 10 ? '0' : '') + d.getHours() + (d.getMinutes() < 10 ? '0' : '') + d.getMinutes() + (d.getSeconds() < 10 ? '0' : '') + d.getSeconds() + milliseconds);

var len = d.getTime();

var offset = d.getTimezoneOffset() * 60000;

var utcTime = len + offset;

d = new Date(utcTime);