Error with .animate() on plain object

[dmethvin]

​https://github.com/jquery/api.jquery.com/issues/514

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Not sure if $.animate intend to support generic object. The code below raise exception "Uncaught TypeError: Cannot use 'in' operator to search for 'opacity' in undefined"

var s = { opacity: 1 };
$(s).animate({opacity: 0}, 5000);

But it try to use $.css to set the opacity. So if I just change to other name

var s = { opacity2: 1 };
$(s).animate({opacity2: 0}, 5000);

and it works.

I guess it might be resolvable If jquery can detect if it's the html object or not. But not sure if $.animate intend to only support html object.

[Timmy Willison]

If we support this, we should support it everywhere. In other words, we should have tests for it everywhere. I think we already do in some places, but the point is let's not just add tests for .animate().

[gibson042]

From ​http://api.jquery.com/animate/:

The .animate() method allows us to create animation effects on any numeric CSS property. The only required parameter is a plain object of CSS properties. This object is similar to the one that can be sent to the .css() method, except that the range of properties is more restrictive.

So we're not explicitly supporting .animate of plain-object properties in our documentation, but this is actually a bug in the underlying jQuery.Animation (for which we do have ​unit tests).

The issue appears to be a problematic interaction with jQuery.cssNumber and unit conversion in the ​default tweener. My inclination is to ignore units unless tween.elem.nodeType === 1, because I don't think there's much of a case (to intentionally understate what's already a dusty corner of the API) for animating non-numeric properties on plain objects... thoughts?

[Timmy Willison]

Since we have unit tests in this area already, I'd mark this as a regression that should be fixed.

[dmethvin]

Agreed. Thanks for the analysis @gibson042!

[m_gol]

Migrated to ​https://github.com/jquery/jquery/issues/1776