function calcTime(city, offset) {
d = new Date();
utc = d.getTime() + (d.getTimezoneOffset() * 60000);
nd = new Date(utc + (3600000*offset));
return "The local time in " + city + " is " + nd.toLocaleString();
}
// get Bombay time
console.log(calcTime('Bombay', '+5.5'));
// get Singapore time
console.log(calcTime('Singapore', '+8'));
// get London time
console.log(calcTime('London', '+1'));
Just change the offset to that city and it will calculate current time for that timezone.