Animating background-position fails in IE8

[lgarvey]

I'm attempting to animate a background image. As per the following jsfiddle:

 http://jsfiddle.net/vEaMd/2/

This fails in IE8 ultimately because

 jQuery.css('backgroundPositionX')

on the div returns "right". In chrome it returns "100%" and in firefox it returns nothing. This breaks the animation since it cannot retrieve the starting position of the background to be animated.

The $.css inconsistency can be easily tested using the following jsfiddle:

 http://jsfiddle.net/Zqj7t/

If someone can point me towards a jQuery test that fixes a similar cross-browser inconsistency I'd gladly write up a proper test-case and submit a patch via github

[dmethvin]

#11972 is a duplicate of this ticket.

[dmethvin]

#11973 is a duplicate of this ticket.

[dmethvin]

The W3C has really made a mess of things with backgroundPosition. Normally there are breakout properties that let you get to all the shorthand ones. That doesn't seem to be the case here. We had a pull request and ticket trying to address it, but it got a lot bigger than we wanted it to be and even then I wasn't sure it would handle all the permutations of backgroundPosition.

Would this solve your use case?

 https://github.com/brandonaaron/jquery-cssHooks/blob/master/bgpos.js

[lgarvey]

My actual problem is that animate breaks in IE8 (I haven't tested in other versions of internet explorer) but works fine in FF, Chrome and Safari. This is because the animate function ends up relying on $.css to retrieve a starting position for the animation and assumes that calling $.css will return either nothing (or empty-string) which is what firefox returns or a numerical value, returned by chrome and safari.

Something along the lines of:

 https://github.com/lengarvey/jquery/commit/51e070009d53c3b17c627d7f90f07860f74fa34e

Should fix the issue (completely untested and commit not performed on a topic branch either. I probably should have gisted it)

[gibson042]

 https://github.com/jquery/jquery/pull/836

[Richard Gibson]

Fix #11971: force numeric animation start to be numeric, closes gh-836.

Changeset: 1793eab32bc8a00b2ad041c9b10ad3bdd2bec702

[Richard Gibson]

Fix #11971 unit test in browsers lacking backgroundPositionX.

Closes gh-850.

Changeset: 376f4e8cf637e76445082d7fdb88ab420d488b5c