Replacing Nodes Error. The node to be replaced is not a child of this node

In replaceChild, the new node is the first argument, not the second. You have them backwards.

parentNode.replaceChild(newNode, currentSelectList);

Also, why would you do i--? Isn't that creating an infinite loop?

currentSelectList.replaceWith(newNode)

Use modern vanilla JS! Way better/cleaner than before. Generic form:

target.replaceWith(element);

developer.mozilla.org

Can I Use - 94% May 2020