Collections expose private state via iteration callbacks.

[DominoPivot]

Naively forwarding a callback function to a private collection inside a signaling wrapper exposes it to untracked reads and writes.

Taking SignalMap as an example, instead of:

forEach (fn) {
  this.collection.get();
  this.vals.forEach(fn);
}

...you probably want to pass the signaling collection to the callback:

forEach (fn) {
  this.collection.get();
  this.vals.forEach((v, k) => fn(v, k, this));
}

[DominoPivot]

You may also want to support the thisArg argument:

forEach (fn, thisArg) {
  this.collection.get();
  this.vals.forEach((v, k) => fn.call(thisArg, v, k, this));
}