domCopyChildrenExcept.js

// copy current children except a certain child while keeping all refs - a pain in the ass.

let i = oldParent.childNodes.length - 1
for (; i >= 0; i -= 1) {
	const c = oldParent.childNodes[i]

	// whatever, your condition here
	if (c.nodeName.toLowerCase() !== "slot") {
		newParent.appendChild(c)
	}
}

// use var instead of let and const for <ES6