@arturovt thanks for the improvement 👍

I think we should optimize this code path by moving the logic into the stashEventListener function (or a function that manages its assignment). Otherwise, we invoke this code for all listeners all the time, when we only need it in case the event replay feature is enabled (explicitly or via incremental hydration).

I get your comment. I'm wondering whether we should be checking if event replay feature is enabled in this code path and only then stash the event listener. I have no ideas on having that functionality inside the stashEventListener, I mean I don't get how it would technically look like.

If I understand correctly, stashing is called every time when listener is added, basically like this:

Element.prototype.addEventListener = function (
  this: Element,
  type: string,
  listener: EventListenerOrEventListenerObject,
  options?: boolean | AddEventListenerOptions,
) {
  const stash = stashEventListeners.get(appId);
  stash?.(this, type, listener as VoidFunction);
  return originalAddEventListener.call(this, type, listener, options);
};

Another question is, should we clear the stash event listener once the hydration is done to avoid stashing it after it's functioning in the browser?

let stashEventListenerImpl = (
  lView: LView,
  target: RElement,
  eventName: string,
  wrappedListener: EventCallback,
) => {};

export function enableStashEventListenerImpl() {
  stashEventListenerImpl = (
    lView: LView,
    target: RElement,
    eventName: string,
    wrappedListener: EventCallback,
  ) => {
    const appId = lView[INJECTOR].get(APP_ID);
    const stashEventListener = stashEventListeners.get(appId);
    stashEventListener?.(target as RElement, eventName, wrappedListener);
  };
}

And in the code:

stashEventListenerImpl(lView, target, eventName, wrappedListener);

That would avoid an injector lookup and a Map lookup every time the listener() is called unless the replay is enabled.

Yes, the solution described in #59635 (comment) looks great and something that I had in mind as well, thank you 👍