Add optional callback to forceUpdate method

[wyze]

This PR aims to solve #434. I've also added a general forceUpdate is called and rerenders the component test since there didn't seem to be one. Let me know if I placed that in the right test file as I was unsure.

[coveralls]

Coverage increased (+0.004%) to 97.699% when pulling 595dfb4 on wyze:forceupdate-callback into 6c7e70c on developit:master.

[developit]

Awesome, and it's only 7 bytes!

[developit]

LGTM :)

[NekR]

Callback is good, but I got to point out that if you are going to make forceUpdate() async someday, then that's major change (e.g. I rely on it to be sync).

[developit]

Agreed - I was going to suggest that might be worth bringing up, but I'm definitely relying on it being synchronous as well. I don't think we can reasonably do that in the near term.

I'd be curious what the filesize would be with a more naive callback solution since it's always synchronous:

forceUpdate(callback) {
  renderComponent(this, FORCE_RENDER);
  if (callback) callback();
}

(not suggesting that's the right way to go here, just crossed my mind)

[NekR]

@developit yeah, I thought about it too. There is no right way here, both are okay :-) (callback && callback() is smaller than if 😝)

[robertknight]

Thank-you for the contribution 👍 - I have made a couple of suggestions for improving the tests if you have time to address them in a follow-up PR.

[robertknight]

Thanks for adding these tests, although it doesn't actually check that the component got re-rendered. Ideally the test would do something mirroring a simplified real-world use of forceUpdate. Something like:

1. Create a component whose output depends on something other than props/state
2. Render
3. Change the external state
4. Force update
5. Check that the rendered output reflects the updated external state.

[robertknight]

renderCallbacks is an implementation detail which we should avoid in the description. What the test actually does, checking that forceUpdate invokes its callback, is fine though.

[coveralls]

Coverage increased (+0.004%) to 97.699% when pulling bb6da19 on wyze:forceupdate-callback into 2b9d81f on developit:master.