How to get timezone of client machine with JavaScript?

function formatedZone() {
var now = new Date(),
tzo = -now.getTimezoneOffset(),
dif = tzo >= 0 ? ‘+’ : ‘-‘,
pad = function(num) {
var norm = Math.abs(Math.floor(num));
return (norm < 10 ? ‘0’ : ”) + norm;
};
return dif+pad(tzo / 60)+ ‘:’ +pad(tzo % 60);
}