javascript - 如何从同一类javascript中的方法返回对象数组

Question

我是 JavaScript 新手。我想要一个类方法返回由同一类实例化的对象数组。如何做到这一点？

目前，基本上以下是我所讨论的代码的一般结构。

class myClass{
   constructor(name,password,emailid,id) {
    this.name = name;
    this.password = password;
    this.emailid = emailid;
    this.id = id;
  }

  asyncMethod = async()=> {
     //method returns array of objects of same class
  }
}

Answer 1

在类实例化(构造函数 init)时，将当前实例推送到类的 static Array .
通过使用 userInstance.getInstances()(← 这是不好的做法!进一步阅读)或 User.instances

来检索所有实例>

class User {

  static instances = [];

  constructor(name, password, emailid, id) {
    this.name = name;
    this.password = password;
    this.emailid = emailid;
    this.id = id;
    User.instances.push(this); // Push instance into static Class's property
  }

  getInstances() {
    return User.instances; // Return array of instances of same Class
  }
}

const A = new User("Cada", "123", "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="9cffdcffb2ff" rel="noreferrer noopener nofollow">[email protected]</a>", 1);
const B = new User("Roko", "234", "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="0e7c4e7c207c" rel="noreferrer noopener nofollow">[email protected]</a>", 2);
const C = new User("John", "345", "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="395379531753" rel="noreferrer noopener nofollow">[email protected]</a>", 3);

console.log(A.name, B.name, C.name); // "Cada", "Roko", "John"
console.log(A.getInstances());  // [User, User, User]
console.log(myClass.instances); // [User, User, User]

密切相关的答案:https://stackoverflow.com/a/61014433/383904

我无法比 MDN 更好地解释 static 关键字。 :

Neither static methods nor static properties can be called on instances of the class. Instead, they're called on the class itself. (*ac: myClass.instances in the above demo)
Static methods are often utility functions, such as functions to create or clone objects, whereas static properties are useful for caches, fixed-configuration, or any other data you don't need to be replicated across instances.

---

将类的内部公开给实例通常是一种不好的做法。
例如，User 实例不应该能够从其 Class 构造函数继承整个用户列表。
下面是一个使用Static Private # 和 Class Getters get 的轻微变体:

class User {

  static #_instances = []; // Static and private

  constructor(userData) {
    Object.assign(this, userData);
    User.#_instances.push(this);
  }

  static get instances() { // Static to Class
    return [...User.#_instances]; // exposes private (as immutable)
  }
}

const A = new User({name:"Cada", password:"123", emailid:"<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="6a092a094409" rel="noreferrer noopener nofollow">[email protected]</a>", id:1});
const B = new User({name:"Roko", password:"234", emailid:"<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="a9dbe9db87db" rel="noreferrer noopener nofollow">[email protected]</a>", id:2});

console.log(A.name, B.name); // "Cada", "Roko",

console.log(A.instances);            // undefined 😭
console.log(User.instances);         // [User, User] 😎

User.instances.push({name:"EVIL!"}); // 😈  
console.log(User.instances);         // [User, User] 😎