function isObject(obj) {
    return obj !== null && typeof obj === 'object';
}

function reactive(target) {
    if (!isObject(target)) return target;
    const handler = {
        get(target, key, receiver) {
            track(target, key);
            const result = Reflect.get(target, key, receiver);
            return isObject(result) ? reactive(result) : result;
        },
        set(target, key, value, receiver) {
            const oldValue = target[key];
            if (oldValue !== value) {
                const result = Reflect.set(target, key, value, receiver);
                trigger(target, key);
                return result;
            }
        }
    };
    return new Proxy(target, handler);
}

const targetMap = new WeakMap();
const effectStack = [];

function track(target, key) {
    if (effectStack.length) {
        let depsMap = targetMap.get(target);
        if (!depsMap) targetMap.set(target, (depsMap = new Map()));
        let dep = depsMap.get(key);
        if (!dep) depsMap.set(key, (dep = new Set()));
        dep.add(effectStack[effectStack.length - 1]);
    }
}

function trigger(target, key) {
    const depsMap = targetMap.get(target);
    if (depsMap) {
        const effects = new Set([...(depsMap.get(key) || [])]);
        effects.forEach(effect => effect());
    }
}

function watchEffect(effect) {
    effectStack.push(effect);
    try {
        return effect();
    } finally {
        effectStack.pop();
    }
}

// 使用示例
const data = reactive({ count: 0 });
watchEffect(() => {
    console.log(`Count is: ${data.count}`);
});

setTimeout(() => {
    data.count++; // 触发副作用，在控制台打印出新的count值
}, 1000);