I found this lib https://react-hooks.org/docs/useeffectoncewhen but I'm confused. Why does it even existed and in what purpose it's used? Isn't I can achieve the same thing using useEffect?
useEffect(() => {
setTimeout(() => {
setLoading(false);
}, 3000); // Countdown for 3 sec
}, [])
You can do the same thing with useEffect:
"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"
You can also supply a list of dependencies that trigger the effect running again if they change.
useEffect( () => { doSomething() } , [ifThisChangesRunFuncAgain, orThis, ...] )
The hook is useEffectOnceWhen, not just useEffectOnce. Per the source you linked:
Runs a callback effect atmost one time when a condition becomes true
Here's the source code of that hook:
/**
* useEffectOnceWhen hook
*
* It fires a callback once when a condition is true or become true.
* Fires the callback at most one time.
*
* @param callback The callback to fire
* @param when The condition which needs to be true
*/
function useEffectOnceWhen(callback: () => void, when: boolean = true): void {
const hasRunOnceRef = useRef(false);
const callbackRef = useRef(callback);
useEffect(() => {
callbackRef.current = callback;
});
useEffect(() => {
if (when && !hasRunOnceRef.current) {
callbackRef.current();
hasRunOnceRef.current = true;
}
}, [when]);
}
As you can see, it does something more advanced than just being called once at the beginning of the hook: it gets called once the condition passed in becomes true for the first time.