用js的class形式写一段单例的状态管理器

class SingletonStateManager {
constructor() {
if (SingletonStateManager.instance) {
return SingletonStateManager.instance;
}

SingletonStateManager.instance = this;
this.state = {};
}

setState(key, value) {
this.state[key] = value;
}

getState(key) {
return this.state[key];
}
}

const stateManager = new SingletonStateManager();
export default stateManager;