1) .index( selector ) - add variant in which elements set precedes method call; i.e. now it works $("li.myClass").index("li"), and suggested variant - $("li").index("li.myClass");

2) .index (element) - update this variant to allow elements array; i.e. now it works $("li").index(document.getElementsByClassName("myClass")[0]), and updated variant - $("li").index(document.getElementsByClassName("myClass")) (only first element of array would be considered)

Sorry for my english :)