React useEffect but after set state value and only once - reactjs

Question

I'm trying to migrate some of my old componentDidMount code to the new useEffect hooks and I'm having problems figuring out how to emulate the callback behavior of setState
I have an array of stuff that gets pulled from an api, I need to call a function only after the state and been loaded and then only once
Previous code:
ComponentDidMount() {
const response = await getMyArrayFromAPI
this.setState({ myArray }, () => { initializeArray() })
}
Current code:
const [myArray, setMyArray] = useState([])
useEffect(() = {
const response = await getMyArrayFromAPI
setMyArray(response)
}, [])
useEffect(() => {
// one time initialization of data
// initially gets called before myArray has value, when it should be after
// gets called every time myArray changes, instead of only once
}, [myArray])

Answer 1

you can set myArray in the first useEffect function, but if you want to use separate functions you can just check if it's empty
useEffect(() => {
if (!myArray.length) {
// one time initialization
}
}, [myArray])

Answer 2

You can use the state to drive whether or not initializeArray needs to run e.g.
const [array, setArray] = useState(null);
useEffect(() => {
getMyArrayFromAPI.then(data => setArray(data || []));
}, []);
if (array) {
// this will only ever run once as we don't set `array`
// anywhere other than `useEffect`
initializeArray();
}
Depending on what initializeArray actually does, you could run it from inside then but that's entirely up to you.

Answer 3

I guess you could create a custom setState hook to manage your callback
const useMyCustomStateHook = (initState, cb) => {
const [customState, updateCustomState] = useState(initState);
useEffect(() => cb(customState), [customState, cb]);
return [customState, updateCustomState];
};
So you could then have
import React, {useState,useEffect} = from 'react'
const [myArray, setMyArray] = useMyCustomStateHook([], initializeArray)
useEffect(() = {
const response = await getMyArrayFromAPI
setMyArray(response)
}, [])