无法使用静态方法返回的类实例访问类方法

问：

我创建了一个订阅者类来存储订阅者详细信息，并使用静态方法返回该类的实例，但我无法使用该实例设置值

下面是订阅者类：

let _instance;

export class Subscriber {

    constructor(username, password) {
        this._username = username;
        this._password = password;
    }


    setSubscriberId(subscriberId) {
        cy.log(subscriberId);
        this._subscriberId = subscriberId;
    }

    setSessionId(sessionId) {
        this.sessionId = sessionId;
    }


    getUserName = () => {
        return this._username;
    }
    getPassword = () => {
        return this._password;
    }

    getSubsciberId() {
        return this._subscriberId;
    }

    getSessionId() {
        return this.sessionId;
    }


    static createSubscriber(username, password) {
        if (!_instance) {
            _instance = new Subscriber(username, password);
        }
        return _intance;
    }

    static getSubscriber() {
        return _instance;
    }
}

我正在创建块中类的实例并访问块中的实例beforeGiven

before("Create a new subscriber before the tests and set local storage", () => {
    const username = `TestAutomation${Math.floor(Math.random() * 1000)}@sharklasers.com`;
    const password = "test1234";
    subscriberHelpers.createSubscriber(username, password, true).then((response) => {
        cy.log(response);
        Subscriber.createSubscriber(username, password);
        Subscriber.getSubscriber().setSubscriberId(response.Subscriber.Id);
        Subscriber.getSubscriber().setSessionId(response.SessionId);
    }).catch((error) => {
        cy.log(error);
    });
});

Given(/^I launch selfcare app$/, () => {
    cy.launchApp();
});

Given(/^I Set the environemnt for the test$/, () => {
    cy.log(Subscriber.getSubscriber());
    cy.log(Subscriber.getSubscriber().getSubsciberId());
});

这是 Cypress 控制台上的输出

问题：

1. 为什么 subscriberID 为 null，即使我在块中设置它before
2. 如果我打印订阅者对象，为什么我没有看到订阅者 ID

这是订阅者对象的输出