Javascript / Node JS創建單例對象的最佳方法

Question

我完成了我的家庭作業並取得了完美的成績。 但我只是想檢查一下，這是創建單例實例的最佳方式還是其他任何方式：

我使用模塊模式（閉包）創建了一個單例對象，“app.js”

var singleton1 = require('./singletonUser1');
console.dir(singleton1.getlocalvariable());
singleton1.setlocalvariable(20);
console.dir(singleton1.getlocalvariable());

var singleton2 = require('./singletonUser2');
console.dir(singleton2.getlocalvariable());
singleton2.setlocalvariable(30);
console.dir(singleton.getlocalvariable());

實際單例對象（singleton.js）：

var singleton = (function () {
    var localvariable = 10;

    return {
        getlocalvariable: function () {
            console.dir('This is getInstance');
            return localvariable;
        },
        setlocalvariable: function (value) {
            console.dir('This is setlocalvariable');
            localvariable = value;
        },
    };
})();

module.exports = singleton;

然后Singleton對象用戶1（singletonUser1.js）：

var singletonUser1 = (function () {
    var singleton = require('./singleton');

    return {
        getlocalvariable: function () {
            console.dir('This is singletonUser1---getlocalvariable');
            return singleton.getlocalvariable();
        },
        setlocalvariable: function (value) {
            console.dir('This is singletonUser1---setlocalvariable');
            singleton.setlocalvariable(value);
        },
    };
})();

module.exports = singletonUser1;

單例對象用戶2（singletonUser2.js）

var singletonUser2 = (function () {
    var singleton = require('./singleton');

    return {
        getlocalvariable: function () {
            console.dir('This is singletonUser2222---getlocalvariable');
            return singleton.getlocalvariable();
        },
        setlocalvariable: function (value) {
            console.dir('This is singletonUser22222---setlocalvariable');
            singleton.setlocalvariable(value);
        },
    };
})();
module.exports = singletonUser2;

請注意，單用戶1和用戶2，是出於某個目的，根據我的項目，上面只是現實世界問題的原型。

我的問題是，我確信這是創建一個類的單個實例（我使用上面的app.js檢查）。 但這是最好的方法嗎？

Answer 1

 var Singleton = (function(){ function Singleton(){ this.localVariable = 5; } // Object can have instance methods as usually. Singleton.prototype.getLocalVariable = function() { return this.localVariable; }; var instance; return function() { if (!instance) { instance = new Singleton(); } return instance; }; })(); var instance1 = new Singleton(); var instance2 = new Singleton(); console.log(instance1 === instance2); // true console.log(instance1.localVariable, instance2.localVariable); // 5 5 instance1.localVariable = 20; console.log(instance1.localVariable, instance2.localVariable); // 20 20 console.log(instance1.getLocalVariable()); // 20 

Answer 2

這是我的可配置單件服務

 function AdService(name) { console.log('new instance created'); this.name = name || 'defaultName'; this.greet = function () { console.log('hi ' + this.name); } }; function Singleton() { this.instance = null; this.getInstance = function getInstance(name) { if (!this.instance) this.instance = new AdService(name); return this.instance; } } var singleton = new Singleton(); module.exports = function (name) { return singleton.getInstance(name); } 

Answer 3

我發現JavaScript中的單例類有點不穩定，在java中它很清楚，即無論何時創建類的對象，你都得到相同的對象，但在JS中，（至少是IMO）沒有真正的類開始。 （不，ES6課程不計算，回答這個，你能擁有私人屬性嗎？）

你的代碼只是做一個閉包，它可能是下面的代碼並沒有區別：

var localvariable = 10;

function getlocalvariable() {
    console.dir('This is getInstance');
    return localvariable;
};
function setlocalvariable(value) {
    console.dir('This is setlocalvariable');
    localvariable = value;
};
module.exports = {
  getlocalvariable: getlocalvariable,
  setlocalvariable: setlocalvariable
};

也就是說，一天結束時，Singleton只是一種模式，我們的實施方式取決於我們，你的方式沒有什么特別的錯誤。

編輯：一個比我更了解JS的人的單例實現（取自學習JavaScript設計模式 ）

var mySingleton = (function () {

  // Instance stores a reference to the Singleton
  var instance;

  function init() {

    // Singleton

    // Private methods and variables
    function privateMethod(){
        console.log( "I am private" );
    }

    var privateVariable = "Im also private";

    var privateRandomNumber = Math.random();

    return {

      // Public methods and variables
      publicMethod: function () {
        console.log( "The public can see me!" );
      },

      publicProperty: "I am also public",

      getRandomNumber: function() {
        return privateRandomNumber;
      }

    };

  };

  return {

    // Get the Singleton instance if one exists
    // or create one if it doesn't
    getInstance: function () {

      if ( !instance ) {
        instance = init();
      }

      return instance;
    }

  };

})();

var myBadSingleton = (function () {

  // Instance stores a reference to the Singleton
  var instance;

  function init() {

    // Singleton

    var privateRandomNumber = Math.random();

    return {

      getRandomNumber: function() {
        return privateRandomNumber;
      }

    };

  };

  return {

    // Always create a new Singleton instance
    getInstance: function () {

      instance = init();

      return instance;
    }

  };

})();


// Usage:

var singleA = mySingleton.getInstance();
var singleB = mySingleton.getInstance();
console.log( singleA.getRandomNumber() === singleB.getRandomNumber() ); // true

var badSingleA = myBadSingleton.getInstance();
var badSingleB = myBadSingleton.getInstance();
console.log( badSingleA.getRandomNumber() !== badSingleB.getRandomNumber() ); // true

// Note: as we are working with random numbers, there is a
// mathematical possibility both numbers will be the same,
// however unlikely. The above example should otherwise still
// be valid.