isNodeAChild
This helper is not exported by @kousta-ui/helpers in the current codebase.
If you need this behavior, prefer the native DOM API:
const isChild = parent?.contains(child) ?? false;
Recommended replacement
Use Element.contains (or Node.contains) with optional chaining:
const parent = document.getElementById("container");
const target = document.getElementById("button");
const isChild = parent?.contains(target) ?? false;