Inside the callback function , for each item of array , there is an pop operation happening

In callback

when the item = 1 → inside callback there is pop operation → which will delete the arrays last item → now the array becomes → [1,2,0]

when the item = 2 → inside callback there is pop operation → which will delete the arrays last item → now the array becomes → [1,2]

If the elements of array are removed during the every function the removed items are not visited .