useMemo以及部分源码

useMemo以及部分源码

const [count,setCount] = useState(0)

const add = useCallback(() => {
   count++;
  setCount(count)
}, [count]);

const getCount = useMemo(()=>{
  console.log(count)
},[count])

const getOldCount = useMemo(()=>{
  console.log(count)
},[])

function mountMemo(nextCreate,deps) {
  const hook = mountWorkInProgressHook();
  const nextDeps = deps === undefined ? null : deps;
  const nextValue = nextCreate();
  hook.memoizedState = [nextValue, nextDeps];
  return nextValue;
}

function updateMemo<T>(nextCreate,deps) {
  const hook = updateWorkInProgressHook();
  const nextDeps = deps === undefined ? null : deps;
  const prevState = hook.memoizedState;
  if (prevState !== null) {
    if (nextDeps !== null) {
      const prevDeps = prevState[1];
      if (areHookInputsEqual(nextDeps, prevDeps)) {
        return prevState[0];
      }
    }
  }
  const nextValue = nextCreate();
  hook.memoizedState = [nextValue, nextDeps];
  return nextValue;
}