jQuery classList plugin

Re-implementation of jQuery class manipulation methods that utilizes the classList interface.

Compatible with jQuery 1.9+.

Rationale

The DOM spec defines the classList interface, allowing for adding/removing/toggling classes or checking if an element contains a specified class using built-in methods as opposed to manually parsing the className field where classes are separated by spaces.

A couple of test suites comparing both implementations:

1. https://jsperf.com/classlist-v-old-way/18 - small (10) number of classes
2. https://jsperf.com/classlist-v-old-way/19 - large (100) number of classes

jQuery currently doesn't utilize this interface, one of the reasons being it's not supported by Internet Explorer 9 and it doesn't work on SVGs even in IE 11.

Browser support

Note: in browsers that don't fully support the classList interface (e.g. all IE & Android Browser) the plugin falls back to the built-in jQuery implementation so it doesn't break them.

The following browsers can utilize full functionality of this plugin:

1. Chrome (for desktop & Android), Edge, Firefox, Opera: Current -1, Current
2. Safari 7.0+
3. iOS 7.0+

"Current -1, Current" denotes that the current stable version of the browser and the version that preceded it are supported. For example, if the current version of a browser is 24.x, we support the 24.x and 23.x versions.

In fact the code will work in many older versions, too, but they are not actively tested.

Caveats

Supported browsers with the jQuery classList plugin pass the whole jQuery test suite with a few minor exceptions:

1. A few tests that check for extra whitespaces in the class attribute or the presence of the class attribute are failing. This is mostly because in Safari up to version 9.x and in current Firefox & Chrome (at the time of writing this section) classList update steps are not performed correctly and there is no way to control that behavior via the classList interface. Relevant bug reports:
   1. Chrome: https://crbug.com/600964
   2. Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=869788
2. In Safari 7 passing the same class to classList.add in multiple parameters results in duplicated class names in the class attribute which makes another few tests fail. However, classList.remove removes all duplicated classes so this shouldn't be a problem unless you're parsing the className attribute directly by yourself. This has been fixed in Safari 8.