Computing client side time drift

gistfile1.txt

$(document).ready(function() {
   	try {
		$("#btnSession").addClass("active");
		
		var server_time = ${System.currentTimeMillis()};
		var client_time = Date.now();
		var drift = (client_time - server_time) / 1000;
		if (window.performance) {
			if (window.performance.timing) {
				if (window.performance.timing.responseStart) {
					drift = (window.performance.timing.responseStart - server_time) / 1000;
				}
			}
		}
		
		if (Math.abs(drift) > 10) {
			$("#display_drift_date").html(
				i18n("userprofile.drifttime.value", drift) + "<br />" +
				i18n("userprofile.drifttime.server", new Date(server_time)) + "<br />" + 
				i18n("userprofile.drifttime.warn")
			);
			$("#display_drift_date").addClass("alert");
			if (Math.abs(drift) > 30) {
				$("#display_drift_date").addClass("alert-error");
			}
		}
	} catch(err) {
		console.log(err);
	}
});