只允许javascript中的类成员的一个实例 [英] Only allowing one instance of a class member in javascript

问题描述

我正在google map API的前面创建一个帮助器类-只是为了学习.

I am creating a helper class in front of the google map API - just for the sake of learning.

即使某人决定实例化该类的另一个实例，我也只希望在我的类中保留google.maps.Map对象的一个​​实例.

I'd like to keep only one instance of the google.maps.Map object around in my class, even if someone decides to instantiate another instance of the class.

我来自.NET背景，那里的概念很简单-但是我仍然适应javascript(和ES6)，因此非常感谢任何指针.

I'm coming from a .NET background, and the concept is simple there - however I'm still getting acclimated to javascript (and ES6), so any pointers are much appreciated.

这是一个摘要片段(通过评论)来解释我要干什么.

Here's a snippet sort of explaining (through comments) what I'm going for.

class Foo {
    constructor(bar) {
        // If someone else decides to create a new instance
        //  of 'Foo', then 'this.bar' should not set itself again.
        // I realize an instanced constructor is not correct.
        // In C#, I'd solve this by creating a static class, making
        //  'bar' a static property on the class.
        this.bar = bar;
    }
}

推荐答案

我认为这是您想要的:

var instance = null;

class Foo {
  constructor(bar) {
    if (instance) {
      throw new Error('Foo already has an instance!!!');
    }
    instance = this;

    this.bar = bar;
  }
}

或

class Foo {
  constructor(bar) {
    if (Foo._instance) {
      throw new Error('Foo already has an instance!!!');
    }
    Foo._instance = this;

    this.bar = bar;
  }
}

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