Question

I have code like that sequentially:

  var d0 = new Date();
  ... 
  ...
  var d1 = new Date();

  if (d0>d1) {
    console.log("Problem");
  }

first look at it, it is no way d1 older than d0. But I just experienced that 2 days ago in a production server. d1 is older than d0 by few milliseconds. How can it be?

and what is the Date() coming from? is it from V8? or from OS system?

Answer 1

It’d be hard to say without taking a much closer look at your system, but in general remember that programming with date and time libraries can occasionally be really, really strange.

Recommended reading: Falsehoods Programmers believe about time

I recently experienced a similar issue in v8 on a production box, and what (we think) was happening was the network time daemon was changing the system’s clock — as it’s designed to do. So, very occasionally we had some profiling that said our “end time” came before our “start time” because the system clock was getting re-synced by NTP in the middle of the code execution.