rc-util/es/hooks/useMergedState.js

import _slicedToArray from "@babel/runtime/helpers/esm/slicedToArray";
import useEvent from "./useEvent";
import { useLayoutUpdateEffect } from "./useLayoutEffect";
import useState from "./useState";
/** We only think `undefined` is empty */
function hasValue(value) {
  return value !== undefined;
}

/**
 * Similar to `useState` but will use props value if provided.
 * Note that internal use rc-util `useState` hook.
 */
export default function useMergedState(defaultStateValue, option) {
  var _ref = option || {},
    defaultValue = _ref.defaultValue,
    value = _ref.value,
    onChange = _ref.onChange,
    postState = _ref.postState;

  // ======================= Init =======================
  var _useState = useState(function () {
      if (hasValue(value)) {
        return value;
      } else if (hasValue(defaultValue)) {
        return typeof defaultValue === 'function' ? defaultValue() : defaultValue;
      } else {
        return typeof defaultStateValue === 'function' ? defaultStateValue() : defaultStateValue;
      }
    }),
    _useState2 = _slicedToArray(_useState, 2),
    innerValue = _useState2[0],
    setInnerValue = _useState2[1];
  var mergedValue = value !== undefined ? value : innerValue;
  var postMergedValue = postState ? postState(mergedValue) : mergedValue;

  // ====================== Change ======================
  var onChangeFn = useEvent(onChange);
  var _useState3 = useState([mergedValue]),
    _useState4 = _slicedToArray(_useState3, 2),
    prevValue = _useState4[0],
    setPrevValue = _useState4[1];
  useLayoutUpdateEffect(function () {
    var prev = prevValue[0];
    if (innerValue !== prev) {
      onChangeFn(innerValue, prev);
    }
  }, [prevValue]);

  // Sync value back to `undefined` when it from control to un-control
  useLayoutUpdateEffect(function () {
    if (!hasValue(value)) {
      setInnerValue(value);
    }
  }, [value]);

  // ====================== Update ======================
  var triggerChange = useEvent(function (updater, ignoreDestroy) {
    setInnerValue(updater, ignoreDestroy);
    setPrevValue([mergedValue], ignoreDestroy);
  });
  return [postMergedValue, triggerChange];
}