Function useReducer

hooks/src/index.js:182–268

(reducer, initialState, init)

 * @returns {[ S, (state: S) => void ]}
 */
export function useReducer(reducer, initialState, init) {
	/** @type {import('./internal').ReducerHookState} */
	const hookState = getHookState(currentIndex++, 2);
	hookState._reducer = reducer;
	if (!hookState._component) {
		hookState._value = [
			!init ? invokeOrReturn(undefined, initialState) : init(initialState),

			action => {
				const currentValue = hookState._nextValue
					? hookState._nextValue[0]
					: hookState._value[0];
				const nextValue = hookState._reducer(currentValue, action);

				if (currentValue !== nextValue) {
					hookState._nextValue = [nextValue, hookState._value[1]];
					hookState._component.setState({});
				}
			}
		];

		hookState._component = currentComponent;

		if (!currentComponent._hasScuFromHooks) {
			currentComponent._hasScuFromHooks = true;
			let prevScu = currentComponent.shouldComponentUpdate;
			const prevCWU = currentComponent.componentWillUpdate;

			// If we're dealing with a forced update `shouldComponentUpdate` will
			// not be called. But we use that to update the hook values, so we
			// need to call it.
			currentComponent.componentWillUpdate = function (p, s, c) {
				if (this._force) {
					let tmp = prevScu;
					// Clear to avoid other sCU hooks from being called
					prevScu = undefined;
					updateHookState(p, s, c);
					prevScu = tmp;
				}

				if (prevCWU) prevCWU.call(this, p, s, c);
			};

			// This SCU has the purpose of bailing out after repeated updates
			// to stateful hooks.
			// we store the next value in _nextValue[0] and keep doing that for all
			// state setters, if we have next states and
			// all next states within a component end up being equal to their original state
			// we are safe to bail out for this specific component.
			/**
			 *
			 * @type {import('./internal').Component["shouldComponentUpdate"]}
			 */
			// @ts-ignore - We don't use TS to downtranspile
			// eslint-disable-next-line no-inner-declarations
			function updateHookState(p, s, c) {
				if (!hookState._component.__hooks) return true;