Discussion on: What should I do if I want to call a function after a state change?

[Alexander B.K.]

Did you consider using useEffect ?

I think you can use useEffect here. You can read in the section : https://reactjs.org/docs/hooks-faq.html#is-it-safe-to-omit-functions-from-the-list-of-dependencies
on how to use it in declaring and calling your funcA function such that it gets called only when the obj state changes.

Because I don't know from where your funcB is called, I leave its declaration as is.
By placing and calling the funcA in a useEffect with the right dependency, in this case your obj variable, the effect is that funcA gets called everytime the obj state changes.

const [obj, setObj] = useState({})

const funcB = (v) => {
  setObj(v)
}

useEffect(() => {
   // funcA should be placed in this useEffect
   const funcA = () => {
       ajax(obj)
    }

    funcA();
 }, [obj]);

[Kunoky]

Because there are many places to modify obj, but I only want to call the funcA after a certain modification, useEffect is not appropriate

[Kunoky]

For example, there is a page to query the list according to conditions. It looks like this

function List() {
  const [condition,setCondition] = useState({})
  const [data,setData] = useState([])
  useEffect(() => {
    listData()
  }, [condition])

  const listData = async () => {
    const res = await ajax(condition)
    setData(res)
  }
  return data
}

Now we add a function to obtain conditions from the server during initialization

function List() {
  const [condition,setCondition] = useState({})
  const [data,setData] = useState([])
  useEffect(() => {
    getCondition()
  }, [])
  useEffect(() => {
    listData()
  }, [condition])

  const listData = async () => {
    const res = await ajax(condition)
    setData(res)
  }
  const getCondition = async () => {
    const res = await ajax()
    setCondition(res)
  }
  return data
}

In this case, listData will be called twice during initialization. Obviously, the first time is useless