How can I call function every 30 seconds on every devices in the same time?

Question

I am gonna try to explain my problem properly. I want to generate number every 30 seconds, like this :

function getRandomNumber(min, max) {
        return Math.floor(Math.random() * (max - min + 1)) + min;
    }
setTimeout(function(){
        getRandomNumber(0,14);
    }, 30000);

This works good, but not same on each device, like if I open the page with this code, I will get random number, but if my friend opens it after e.g. 5 seconds since I have opened the page, there arises delay. Is there any way to fix it? I thought something like getting time server and doing it according to him could work, but I have no idea how to do it.

Answer 1

There is no perfect solution to this problem, here two options:
A simple one and a complicated one wich should be more precise.

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If you have the same time on all devices* you could use new Date().getTime() % 30000 for the first call, so they are all on sync, and then always use constant 30000 in the timeout.

function getRandomNumber(min, max) {
  return Math.floor(Math.random() * (max - min + 1)) + min;
}
setTimeout(function() {
  getRandomNumber(0, 14);
}, new Date().getTime() % 30000); // first time use this

* Timezones won't matter, but the seconds of a minute

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Another way would to let the server pass his time, and then guess the latency to correct the loading time, and use that instad of new Date().getTime()