Browser timezone/dst detection

DetermineBrowserTimezoneIsDST.js

var date = new Date();
var jan = new Date(date.getFullYear(), 0, 1);
var jul = new Date(date.getFullYear(), 6, 1);
// Offset is in minutes
var stdTimezoneOffset = Math.max(jan.getTimezoneOffset(), jul.getTimezoneOffset());

// Convert to local machine timezone for date object in PST
var timezoneDiffFromPST = stdTimezoneOffset - 480;
date += timezoneDiffFromPST * 60 * 60 * 1000;


var isDST = date.getTimezoneOffset() < stdTimezoneOffset;