ES6：超级类不持有状态 [英] ES6: Super class doesn't hold state

问题描述

我正在尝试弄清楚这里发生了什么，因为父/超级类在初始构建之后没有数据。

//导入/服务器/a-and-b.js

  class A {
 constructor（id）{
 //使MongoDB调用并存储在此变量
 // ... 
 this._LocalVariable = FieldFromMongo; 
 console.log（`this._LocalVariable：$ {this._LocalVariable}`）; // =>这有一个很好的价值，即：'Test'
} 
 get LocalVar（）{
 console.log（`this._LocalVariable：$ {this._LocalVariable}`）; // =>从子类调用
时返回this._LocalVariable; 
} 
} 
 
导出类B扩展A {
构造函数（id）{
 super（id）; 
 this.TEST ='这是一个测试'; 
} 
得到THE_Variable（）{
 console.log（`super.LocalVar：$ {super.LocalVar}`）; // =>当
返回super.LocalVar时，它有一个未定义的值; 
} 
 get GETTHEVAR（）{
 return this.TEST; // =>这返回'这是一个测试'
} 
} 
  

//导入/server/factory.js

  import {B} from'imports / server / a-and-b.js'; 
 
 class Factory {
 constructor（）{
 this._factory = new Map（）; 
} 
 BuildInstances（id，cls）{
 let instance = this._factory.get（cls）; 
 
 if（！instance）{
 if（cls ==='B'）{
 instance = new B（id）; 
 this._factory.set（cls，instance）; 
 return instance; 
} 
} 
 else {
 return instance; 
} 
} 
} 
 export let OptsFactory = new Factory（）; 
  

// exports / server / test.js

来自'imports / server / factory.js'的$ {pre> import {OptsFactory}

const B = OptsFactory.BuildInstances（id，'B'）;

const THE_Variable = B.THE_Variable; // =>总是未定义

const TEST = B.GETTHEVAR; // =>总是返回'这是一个测试'


为什么A类不保持状态？

解决方案

这是我发现的：

  A类{
构造函数（id）{
 //使MongoDB调用并存储在此变量中
 // ... 
 this._LocalVariable = FieldFromMongo; 
} 
 get LocalVar（）{
 return this._LocalVariable; 
} 
 GetThatLocalVar（）{
 return this._LocalVariable; 
} 
} 
 
导出类B扩展A {
构造函数（id）{
 super（id）; 
} 
 get Style1（）{
 //引用父取得函数
 return super.LocalVar; // =>当
} 
 get Style2（）{
 //引用父属性
返回super._LocalVariable; // =>当
} 
时，它有一个未定义的值。
 get Style3（）{
 //引用在Parent 
中声明的本地属性返回this._LocalVariable; // =>这个工程
} 
 get Style4（）{
 //引用父没有getter 
返回super.GetThatLocalVar（）; // =>这个工程
} 
 get GETTHEVAR（）{
 return this.TEST; // =>这返回'这是一个测试'
} 
} 
  

所以基本上Style3 Style 4的作品。

I'm trying to figure out what's going on here, as the Parent/Super class does not have data after the initial construction.

// imports/server/a-and-b.js

class A {
  constructor(id) {
    // make MongoDB call and store inside this variable
    // ...
    this._LocalVariable = FieldFromMongo;
    console.log(`this._LocalVariable: ${this._LocalVariable}`); // => This has a good value, ie: 'Test'
  }
  get LocalVar() {
    console.log(`this._LocalVariable: ${this._LocalVariable}`); // => This has a undefined value when called from child class
    return this._LocalVariable;
  }
}

export class B extends A {
  constructor(id) {
    super(id);
    this.TEST = 'THIS IS A TEST';
  }
  get THE_Variable() {
    console.log(`super.LocalVar: ${super.LocalVar}`); // => This has a undefined value when called
    return super.LocalVar;
  }
  get GETTHEVAR() {
    return this.TEST; // => This returns 'THIS IS A TEST'
  }
}

// imports/server/factory.js

import { B } from 'imports/server/a-and-b.js';

class Factory {
  constructor() {
    this._factory = new Map();
  }
  BuildInstances(id, cls) {
    let instance = this._factory.get(cls);

    if (!instance) {
      if (cls === 'B') {
        instance = new B(id);
        this._factory.set(cls, instance);
        return instance;
      }
    }
    else {
      return instance;
    }
  }
}
export let OptsFactory = new Factory();

// imports/server/test.js

import { OptsFactory } from 'imports/server/factory.js'

const B = OptsFactory.BuildInstances(id, 'B');

const THE_Variable = B.THE_Variable; // => always undefined

const TEST = B.GETTHEVAR; // => Always returns 'THIS IS A TEST'

Why does class A not keeping state?

解决方案

This is what I found:

class A {
  constructor(id) {
    // make MongoDB call and store inside this variable
    // ...
    this._LocalVariable = FieldFromMongo;
  }
  get LocalVar() {
    return this._LocalVariable;
  }
  GetThatLocalVar() {
    return this._LocalVariable;
  }
}

export class B extends A {
  constructor(id) {
    super(id);
  }
  get Style1() {
    // Reference to Parent get function
    return super.LocalVar; // => This has a undefined value when called
  }
  get Style2() {
    // Reference to Parent property
    return super._LocalVariable; // => This has a undefined value when called
  }
  get Style3() {
    // Reference to local Property that is declared in Parent
    return this._LocalVariable; // => This works
  }
  get Style4() {
    // Reference to Parent without the getter
    return super.GetThatLocalVar(); // => This works
  }
  get GETTHEVAR() {
    return this.TEST; // => This returns 'THIS IS A TEST'
  }
}

So basically the thing that works is Style3 Style 4 work.

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