Recent change: `set`, `get` no longer functional in `ondestroy`

[TehShrike]

Somewhere between 1.29 and 1.32 (I think mostly in #755), set and get turned into noop by the time ondestroy is called.

I have some use cases for calling both those methods (especially get) in ondestroy, so it would be nice to leave them functional until after it was called.

[Conduitry]

From what I gathered in gitter, your use case was mainly storing listener deregisterers on the component and then calling them in ondestroy. I recently had to deal with something like that, and how I handled it was

oncreate() {
  this.on('destroy', registerListenerAndReturnDeregisterer())
}

i.e., I didn't officially register an ondestroy hook, I just attached a destroy lifecycle event handler in the oncreate hook, where I already had access to the deregisterer. Not to say that this is the only reason for wanting to access get, or that what you're suggesting isn't a good idea - it's just another idea that might be useful.

[TehShrike]

That is an excellent tip.

[shanewwarren]

I just ran into this issue as well and I'm not 100% on how to proceed. I see that @TehShrike and @Conduitry have a work around which is great. However, is this going to be the expected behavior of ondestroy moving forward? Or is it a bug?

[Rich-Harris]

I guess we just need to figure out exactly what the behaviour should be, and implement it. E.g. is it just making this change?

export function destroy(detach) {
-  this.destroy = this.set = this.get = noop;
+ this.destroy = noop;
  this.fire('destroy');
+  this.set = this.get = noop;

[shanewwarren]

Not allowing any state changes when a component is being unmounted to me seems
pretty consistent with most other view libraries. For instance, in React setState is not allowed in componentWillUnmount.

With regards to this.get though - I'm not entirely sure.

I think I was only using this.get often in ondestroy was because it was available. At least in the use cases I've come across this.get hasn't been strictly necessary though.

I'd opt for (but I'm sure others might have a much better idea here):

export function destroy(detach) {
  this.destroy = this.set = noop;
  this.fire('destroy');
  this.get = noop;
  ...

My 2 cents, and thanks for everything Rich!

[TehShrike]

I actually do have a use case for set in ondestroy - I have a component that tracks visibility, and uses two-way binding to keep a visible property up to date, and I make sure to set visible to false in ondestroy just so there isn't some state around somewhere that thinks that item is still visible somehow.

I would rather the component was still "fully functional" until after ondestroy.