How does UTC work with Javascript and computers with wrong times?

I have been writing some JavaScript code that relies upon universal time. I have been doing this online with two computers. One of which is 24 minutes behind the other.

Example:

Computer 1: 25/07/2020, 21:57     Computer 2: 25/07/2020, 22:21

When both computers enter a UTC number they are still the equivalent of 24 minutes apart.

Computer 1: 1595710054892    Computer 2: 1595711497605

This difference in time is causing problems with my programme as it relies upon timed notifications.

Is there anyway to correct for this or will I just have to hope that computers that use my JavaScript code will all have the same time within their respective timezone?

Solution

If you can't trust the clock on the computer (which is, frankly, shocking for a network-connected system in 2020) then you need to get the current time from somewhere else.

The standard way to do this would be to use the Network Time Protocol.

A quick Google turns up this JavaScript implementation of an NTP client:

var ntpClient = require('ntp-client');
 
ntpClient.getNetworkTime("pool.ntp.org", 123, function(err, date) {
    if(err) {
        console.error(err);
        return;
    }
 
    console.log("Current time : ");
    console.log(date); // Mon Jul 08 2013 21:31:31 GMT+0200 (Paris, Madrid (heure d’été))
});

If you're dealing with JS in a browser, you won't be able to use the NTP protocol directly so you would need to proxy the request via some server-side code which would lose some accuracy (but assuming a reasonable network connection, that would be in the order of a few seconds rather than 10s of minutes).