ul alt2 should be aaa3 but becomes aaa0 why?
$(" .item").each(function(e){
tt=$(this);
tt.attr("alt",e);
$(this).closest('.item').attr('alt2', 'aaa'+$(this).attr('alt') );
})<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.6.3/jquery.min.js"></script>
<ul class='item' alt2=''>
<li class='item'>aaaa</li>
<li class='item'>aaaa</li>
<li class='item'>aaaa</li>
</ul>ul alt2 should be aaa3 but becomes aaa0 why?
Not a bug in .closest(), but I suppose it could be unintuitive. Look closely at the description in the documentation (emphasis mine):
For each element in the set, get the first element that matches the selector by testing the element itself and traversing up through its ancestors in the DOM tree.
In this case the element itself is matching the selector:
$(this).closest('.item')
You could use .parents instead:
$(this).parents('.item')
Or use a more specific selector:
$(this).closest('ul.item')
eis the index of the loop, since theulis the first element of the selectionewill be 0 in that case.