blocks|key|141066|text|您需要静态属性，而不是实例属性this.instance。它将可由QuestionnaireManager.instance引用访问。但是..。在Javascript中实现经典的GOF单例是非常罕见的.强迫自己在vim中开发UI，并感觉自己是“真正的开发人员”:)|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|141067|entityMap^0|F|D|X|T|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|M|8|@]|D|@]|E|$]]]|G|$]]

<p>You need a static property, not instance property <code>this.instance</code>. It will be accessable by <code>QuestionnaireManager.instance</code> reference. But... it is sooo rare case to implement classical GOF singleton in Javascript... kind of enforcing yourself to develop UI in vim and feel yoursefl as "true develper" :)</p>


blocks|key|141119|text|这不是在ES6中实现Singleton的正确方法。正确的方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|141120|​|141121|class+QuestionnaireManager+{
++constructor()+{
++++if+(QuestionnaireManager._instance)+{
++++++throw+new+Error("Singleton+classes+can't+be+instantiated+more+than+once.")
++++}
++++QuestionnaireManager._instance+=+this;

++++//+...+your+rest+of+the+constructor+code+goes+after+this
++}
}

var+managerOne+=+new+QuestionnaireManager()
var+managerTwo+=+new+QuestionnaireManager()+//+Throws+error|code-block|syntax|javascript|141122|141123|或者，如果不希望在第二个实例创建时抛出错误，只需返回最后一个实例，如下所示：|141124|141125|class+QuestionnaireManager+{
++constructor()+{
++++if+(QuestionnaireManager._instance)+{
++++++return+QuestionnaireManager._instance
++++}
++++QuestionnaireManager._instance+=+this;

++++//+...+your+rest+of+the+constructor+code+goes+after+this
++}
}

var+managerOne+=+new+QuestionnaireManager()
var+managerTwo+=+new+QuestionnaireManager()

console.log(managerOne+===+managerTwo)+//+logs+"true"|141126|141127|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|T|8|@]|9|@]|A|$G|H]]|$1|I|3|C|5|6|7|U|8|@]|9|@]|A|$]]|$1|J|3|K|5|6|7|V|8|@]|9|@]|A|$]]|$1|L|3|C|5|6|7|W|8|@]|9|@]|A|$]]|$1|M|3|N|5|F|7|X|8|@]|9|@]|A|$G|H]]|$1|O|3|C|5|6|7|Y|8|@]|9|@]|A|$]]|$1|P|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|Q|$]]

<p>That ain't the right way to implement Singleton in ES6. The correct way:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>class QuestionnaireManager {
  constructor() {
    if (QuestionnaireManager._instance) {
      throw new Error("Singleton classes can't be instantiated more than once.")
    }
    QuestionnaireManager._instance = this;

    // ... your rest of the constructor code goes after this
  }
}

var managerOne = new QuestionnaireManager()
var managerTwo = new QuestionnaireManager() // Throws error</code></pre>
</div>
</div>
</p>

<p>Or, if you don't want an error to be thrown on second instance creation you can just return the last instance, like so:</p>

<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-js lang-js prettyprint-override"><code>class QuestionnaireManager {
  constructor() {
    if (QuestionnaireManager._instance) {
      return QuestionnaireManager._instance
    }
    QuestionnaireManager._instance = this;

    // ... your rest of the constructor code goes after this
  }
}

var managerOne = new QuestionnaireManager()
var managerTwo = new QuestionnaireManager()

console.log(managerOne === managerTwo) // logs "true"</code></pre>
</div>
</div>
</p>


blocks|key|141155|text|在javascript中，您可以导出类的实例以生成单例。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|141156|//+questionnaire-manager.js
class+QuestionnaireManager+{

++constructor()+{
++}
}

module.exports+=+new+QuestionnaireManager()|code-block|syntax|javascript|141157|然后，当您调用require('questionnaire-manager')时，您将始终得到相同的实例。|offset|length|style|CODE|141158|entityMap^0|0|0|7|W|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@$I|R|J|S|K|L]]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

<p>In javascript you can export an instance of a class to make a singleton</p>

<pre class="lang-js prettyprint-override"><code>// questionnaire-manager.js
class QuestionnaireManager {

  constructor() {
  }
}

module.exports = new QuestionnaireManager()
</code></pre>

<p>Then when you call <code>require('questionnaire-manager')</code> you'll always get the same instance.</p>


blocks|key|1165437|text|和Mikel+B.的答案一样，只有在更短的语法中才能回答。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|1165438|module.exports+=+new+class+foo+{..}|code-block|syntax|javascript|1165439|entityMap^0|0|S|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@$9|N|A|O|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|P|8|@]|D|@]|E|$I|J]]|$1|K|3|-4|5|6|7|Q|8|@]|D|@]|E|$]]]|L|$]]

<p><strong>Like Mikel B.'s answer only in a shorter syntax</strong></p>
<pre><code>module.exports = new class foo {..}
</code></pre>


blocks|key|2767923|text|//+Singleton.js

class+Singleton+{
++++constructor(){
++++++++if(Singleton._instance){
++++++++++++console.warn("already+created!");
++++++++++++return+Singleton._instance;
++++++++}

++++++++Singleton._instance+=+this;

++++++++console.log("singleton+created");

++++++++this._createdTime+=+new+Date();
++++}

++++static+instance()+{
++++++++if(!Singleton._instance){
++++++++++++return+new+Singleton();
++++++++}

++++++++return+Singleton._instance;
++++}

++++createdTime()+{
++++++++return+this._createdTime.toISOString();
++++}
}

Singleton._instance+=+null;

export+default+Singleton;

//+main.js

import+Singleton+from+"./Singleton"

const+a+=+new+Singleton();
const+b+=+new+Singleton();
const+c+=+Singleton.instance();

console.log(a.createdTime());
console.log(b.createdTime());
console.log(c.createdTime());|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2767924|产出将|unstyled|2767925|📷|atomic|offset|length|2767926|​|2767927|entityMap|0|IMAGE|mutability|IMMUTABLE|imageUrl|https://developer.qcloudimg.com/http-save/yehe-900000/4b56833dab9f9e74e4a219aa31acfba5.png|imageAlt^0|0|0|0|1|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|X|8|@]|9|@]|A|$]]|$1|G|3|H|5|I|7|Y|8|@]|9|@$J|Z|K|10|1|11]]|A|$]]|$1|L|3|M|5|F|7|12|8|@]|9|@]|A|$]]|$1|N|3|-4|5|F|7|13|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U|V|-4]]]]

<pre><code>// Singleton.js

class Singleton {
    constructor(){
        if(Singleton._instance){
            console.warn(&quot;already created!&quot;);
            return Singleton._instance;
        }

        Singleton._instance = this;

        console.log(&quot;singleton created&quot;);

        this._createdTime = new Date();
    }

    static instance() {
        if(!Singleton._instance){
            return new Singleton();
        }

        return Singleton._instance;
    }

    createdTime() {
        return this._createdTime.toISOString();
    }
}

Singleton._instance = null;

export default Singleton;

// main.js

import Singleton from &quot;./Singleton&quot;

const a = new Singleton();
const b = new Singleton();
const c = Singleton.instance();

console.log(a.createdTime());
console.log(b.createdTime());
console.log(c.createdTime());

</code></pre>
<p>Output would be
<a href="https://i.stack.imgur.com/fRPMj.png" rel="noreferrer"><img src="https://i.stack.imgur.com/fRPMj.png" alt="enter image description here" /></a></p>


<p>I am working on a large project where I have multiple managers to handle different tasks, I need an only a single object of these managers to be created when I start the app, </p>

<p>I came across this method of Singleton creation </p>

<pre><code>class QuestionnaireManager {

  constructor() {
    if (this.instance) {
      return;
    }
    this.instance = this;
  }
}
</code></pre>

<p>Is this an acceptable way, is there any downside, I am coming from <code>JAVA</code> <code>Kotlin</code> background and this seems to simple to be true where we have so much to deal in case of singletons in other languages. (Most of those cases have to deal with multi-threading but as JS is single-threaded so I think this would be sufficient way)</p>

<p>Still need opinion on best practices, or any other Dependency Injection methods where we don't even rely on Singleton but create the object once and reuse all over the project with dependency injections.</p>

<p>I would like to know the opinion of sensie in JS.</p>


How to create singleton classes in Javascript?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

我正在做一个大型项目，在这个项目中，我有多个管理人员来处理不同的任务，在启动应用程序时，我只需要创建这些管理器的一个对象，我偶然发现了一种新的创作方法class QuestionnaireManager {  constructor() {    if (this.instance) {      return;   ...

问如何在Javascript中创建单例类？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问如何在Javascript中创建单例类？EN