Issue number: N/A
---------
<!-- Please do not submit updates to dependencies unless it fixes an
issue. -->
<!-- Please try to limit your pull request to one type (bugfix, feature,
etc). Submit multiple pull requests if needed. -->
## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
While debugging #28186, Maria and I identified that Ionic's lifecycle
event listeners (`ionViewWillEnter`, etc.) were being registered
multiple times on the same `.ion-page` element. This resulted in
problematic behavior, where a user's implementation of our lifecycle
hooks, would execute their callback multiple times.
```ts
useIonViewWillEnter(() => {
// This is called 2x for every time the `ionViewWillEnter` event is emitted (in React 18, dev mode)
console.log('hello world');
});
```
When the Ionic lifecycle event listeners are registered in React, we
bind the scope of the class to the callback function. When removing the
event listener we additional use the `.bind` syntax.
```tsx
componentDidMount() {
element.addEventListener('ionViewWillEnter', this.ionViewWillEnter.bind(this));
}
componentWillUnmount() {
// This creates a new instance of the function to remove! It doesn't remove the original event listener.
element.removeEventListener('ionViewWillEnter', this.ionViewWillEnter.bind(this));
}
```
The `.bind` method returns a new instance of the function. This means in
the implementation we are creating a new instance of the function when
both adding and removing the event listener - resulting in the
`removeEventListener` to never remove the original event listener.
This behavior only occurred in React 18 in dev mode, as a result of the
mount/unmount behavior running 2x for `useEffect` hooks.
## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->
- Ionic lifecycle event listeners are removed from element references
when they are unmounted.
- User's lifecycle callback methods are only invoked once per event
emission.
|Before|After|
|----|----|
|<img alt="CleanShot 2023-10-09 at 18 32 08@2x"
src="https://github.com/ionic-team/ionic-framework/assets/13732623/53f2ef5d-5900-4a84-b427-fa6c9d35d081">|<img
alt="CleanShot 2023-10-09 at 18 29 37@2x"
src="https://github.com/ionic-team/ionic-framework/assets/13732623/c8a9a657-a0bf-4d6d-9f21-a41a686de490">|
## Does this introduce a breaking change?
- [ ] Yes
- [x] No
<!-- If this introduces a breaking change, please describe the impact
and migration path for existing applications below. -->
## Other information
<!-- Any other information that is important to this PR such as
screenshots of how the component looks before and after the change. -->
---------
Co-authored-by: Maria Hutt <maria@ionic.io>
Co-authored-by: Amanda Johnston <90629384+amandaejohnston@users.noreply.github.com>
