Comments (13)
Looks good!
Still needs tests for useEffect()
with no second argument, and with []
- let's leave this issue open until all the tests are in place.
from fre.
useEffect(() => {
function handleStatusChange(status) {
setIsOnline(status.isOnline)
}
ChatAPI.subscribeToFriendStatus(props.friend.id, handleStatusChange)
return function cleanup() {
ChatAPI.unsubscribeFromFriendStatus(props.friend.id, handleStatusChange)
}
}
The use case from the react document looks like when useEffect returns a function, we execute it
The function contains unmouted logic
Am I correct?
from fre.
Yes:
the function passed to useEffect may return a clean-up function [...] The clean-up function runs before the component is removed from the UI to prevent memory leaks. Additionally, if a component renders multiple times (as they typically do), the previous effect is cleaned up before executing the next effect
from fre.
(Preact hooks are a good source of reference, as the code is very simple and easy to understand.)
from fre.
Well, I need to think carefully about the correct implementation here. My previous understanding may be insufficient.~
from fre.
@mindplay-dk I refactored the useEffect, and now it should be able to resolve these two issues #63 #64
from fre.
supported Now!
from fre.
Looks good, just one small deviation from how React works - from the description in the yellow note box on this page:
If you want to run an effect and clean it up only once (on mount and unmount), you can pass an empty array ([]) as a second argument. This tells React that your effect doesn’t depend on any values from props or state, so it never needs to re-run.
So, to summarize:
useEffect(f) // ✅ effect (and clean-up) every time
useEffect(f, []) // ❌ effect (and clean-up) only once in a component's life
useEffect(f, [x]) // ✅ effect (and clean-up) when property x changes
from fre.
Where is the deviation? The summarize is right 😆
from fre.
@mindplay-dk I tried the use case of react, which would not execute when the array was empty.
useEffect(f, []) // ✅ return function( such as clean up) should not run.
So fre's current behavior should be consistent with react
from fre.
I tried the use case of react, which would not execute when the array was empty.
The clean-up function of an effect always runs - the question is only when.
With an empty array, the clean-up function should run only once, when the component is destroyed.
from fre.
I didn't even notice this detail. I've fixed it and it works now 💯
from fre.
We have tests for this now. Closing!
from fre.
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from fre.