Question

What’s the best way to get monotonically increasing time in JavaScript? I’m hoping for something like Java’s System.nanoTime().

Date() obviously won’t work, as it’s affected by system time changes.

In other words, what I would like is for a <= b, always:

a = myIncreasingTime.getMilliseconds();
...
// some time later, maybe seconds, maybe days
b = myIncreasingTime.getMilliseconds();

At best, even when using the UTC functions in Date(), it will return what it believes is the correct time, but if someone sets the time backward, the next call to Date() can return a lesser value. System.nanoTime() does not suffer from this limitation (at least not until the system is rebooted).

Modification: [2012-02-26: not intended to affect the original question, which has a bounty]

I am not interested knowing the “wall time”, I’m interested in knowing elapsed time with some accuracy, which Date() cannot possibly provide.

Answer 1

You could use window.performance.now() – since Firefox 15, and window.performance.webkitNow() – Chrome 20]

var a = window.performance.now();
//...
var delay = window.performance.now() - a;