[beedrillzzzzz]

Fairly common: triggering a side-effect that uses some state value, only when a different piece of state changes.

useEffect(() => { doSomething(someState) }, [otherState])

[jhardy54]

Sorry, there might be a misunderstanding —- I’m looking for an example of when the dependency array needs to be [], is that what you posted?

[naught0]

The example supplied is what I was trying to get at.

An empty dependency array means that the effect runs only once on mount. Same with memos and callbacks -- the value should remain stable. Here's a real world example of how I populate some state based on url query params:

https://github.com/Naught0/combinator/blob/master/frontend/s...

I may end up using a more robust routing solution to keep in sync with query params if I ever want to spend the effort, but this is a naive solution that works alright.

A more simplified, generic example could be:

  const [foo, setFoo] = useState();
  useEffect(() => {
    setFoo("bar");
  }, []); // The eslint rule wants setFoo here despite the value being stable

[beedrillzzzzz]

Yeah maybe I didn’t follow exactly, I meant this as a common example of when the hook dependencies rules must be ignored.