Why is my setTimeout accelerated when I have several tabs open for my site?

Question

I have a timer that counts down every second. It works fine until the user opens 3 or 4 tabs of my site, after which the newest tab timer will have double or triple speed. Currently, I can only reproduce the error in IE8. I previously used setInterval and could also reproduce the error in Firefox.

I actually use FBJS (Facebook Javascript), so I will just give the pseudo code.

function countDown() { ... setTimeout(function() { countDown() }, 1000); } countDown(); 

However, what I'm really looking for is more theoretical. I know that browsers can try to catch up with setInterval, but how can this affect multiple tabs for setTimeout?

Answer 1

This whole situation is very strange. The only scenario that comes to mind when it makes any sense is the one where the browser tries to “smooth out” the setTimeouts self-healing period, the same as for setInterval, and the code that does this actually confuses the timers in different windows with each other.

I don’t know if this is possible, especially with Facebook, but an interesting test would be to give each instance a randomized name for the countDown function and see if it makes any difference, for example:

 <?php $timerTag = rand(1, 1000); ?> function countDown<?php echo $timerTag ?>() { ... setTimeout(function() { countDown<? php echo $timerTag ?>() }, 1000); } countDown<?php echo $timerTag ?>(); 

If this changes the observed behavior, it speaks of a scenario that I have in mind. (And perhaps provides a way to solve the problem.)