Javascript animation slows down when tab loses focus

👁 Image	Duncan Loveday Reporter
	Description • 13 years ago

User Agent: Mozilla/5.0 (Windows NT 6.1; rv:21.0) Gecko/20100101 Firefox/21.0 (Beta/Release) Build ID: 20130511120803 Steps to reproduce: (1) Load the attached test case in tab 1 (2) Click the Start button (3) A popup opens in which a counter is displayed. The counter counts up. (4) Move the popup to a location where it will not be obscured by the main browser window (5) In the main browser window, select a different tab, i.e. a tab other than tab 1. Actual results: The counting up slows down radically. Expected results: The counting should continue at the same speed.

👁 Image	Duncan Loveday Reporter
	Comment 1 • 13 years ago

Possible duplicate of bug 665000 though I thought the behaviour changed more recently than that.

👁 Image	Duncan Loveday Reporter
	Comment 2 • 13 years ago

👁 Image	Duncan Loveday Reporter
	Updated • 13 years ago

👁 Image	Duncan Loveday Reporter
	Comment 3 • 13 years ago

Hmmm I think this must be by design, the behaviour seems to be controlled by dom.min_background_timeout_value. Set that to a low value and the animation works OK even in a background tab. This is a bit annoying - impacts some code I have that uses Neil Mix's threading library which is based on setTimeout (http://www.neilmix.com/2007/02/07/threading-in-javascript-17/). Start some javascript running and go off to another tab and the javascript slows to a crawl.

👁 Image	Boris Zbarsky [:bzbarsky]
	Comment 4 • 13 years ago

This is very much purposeful: we throttle timeouts in background tabs to a 1000ms minimum (compared to 4ms minimum for foreground tabs), to keep them from chewing up CPU. And yes, bug 665000 is about pretty much the same issue. Note that other UAs have the same behavior at this point, for similar reasons.

👁 Image	Boris Zbarsky [:bzbarsky]
	Updated • 13 years ago

👁 Image	Nobody; OK to take it and work on it Assignee
	Updated • 7 years ago