jquery filtering has + not

Question

Okay I have list items, some have a span, some not.
On my event I want to add the span when they don\'t have any yet.

has() works fine, but

Answer 1

The accepted answer works well, if you don't want to filter out only those elements which do have the spans as direct children.

As the :has() and the .has() loop over all descendants, not just the children.

In that case, you have to use a function

$("li").not(function() {
    // returns true for those elements with at least one span as child element
    return $(this).children('span').length > 0 
}).each(function() { /* ... */ })