Javascript - Calculating Elapsed Time

// using static methods
var start = Date.now();
// the event you'd like to time goes here:
doSomethingForALongTime();
var end = Date.now();
var elapsed = end - start; // time in milliseconds

// if you have Date objects
var start = new Date();
// the event you'd like to time goes here:
doSomethingForALongTime();
var end = new Date();
var elapsed = end.getTime() - start.getTime(); // time in milliseconds"

// About Date()
new Date()
new Date(milliseconds)
new Date(dateString)
new Date(year, month, date [, hour, minute, second, millisecond ])

today = new Date();
birthday = new Date("December 17, 1995 03:24:00");
birthday = new Date(1995,11,17);
birthday = new Date(1995,11,17,3,24,0);