Javascript:最好的Singleton模式

Question

可能重复:
在JavaScript中实现单例的最简单/最简洁的方法？

我将这种模式用于单身人士,在单例中,单身人士是PlanetEarth:

var NAMESPACE = function () {

    var privateFunction1 = function () {
        privateFunction2();
    };

    var privateFunction2 = function () {
        alert('I\'m private!');
    };

    var Constructors = {};

    Constructors.PlanetEarth = function () {
        privateFunction1();
        privateFunction2();
    };

    Constructors.PlanetEarth.prototype = {
        someMethod: function () {
            if (console && console.log) {
                console.log('some method');             
            }
        }
    };

    Constructors.Person = function (name, address) {
        this.name = name;
        this.address = address;
    };

    Constructors.Person.prototype = {
        walk: function () {
            alert('STOMP!');
        }
    };

    return {
        Person: Constructors.Person, // there can be many
        PlanetEarth: new Constructors.PlanetEarth() // there can only be one!
    };

}();

由于PlanetEarth的构造函数仍然是私有的,因此只能有一个.

现在,有些东西告诉我,这种自煮熟的东西不是最好的东西,主要是因为我没有接受过学术教育,而且我倾向于以愚蠢的方式解决问题.你会建议什么作为一种更好的替代方法,哪种更好被定义为风格更好和/或更强大？

Answer 1

(1)更新2019年:ES7版本

class Singleton {
    static instance;

    constructor() {
        if (instance) {
            return instance;
        }

        this.instance = this;
    }

    foo() {
        // ...
    }
}

console.log(new Singleton() === new Singleton());

(2)ES6版本

class Singleton {
    constructor() {
        const instance = this.constructor.instance;
        if (instance) {
            return instance;
        }

        this.constructor.instance = this;
    }

    foo() {
        // ...
    }
}

console.log(new Singleton() === new Singleton());

找到最佳解决方案:http: //code.google.com/p/jslibs/wiki/JavascriptTips#Singleton_pattern

function MySingletonClass () {

  if (arguments.callee._singletonInstance) {
    return arguments.callee._singletonInstance;
  }

  arguments.callee._singletonInstance = this;

  this.Foo = function () {
    // ...
  };
}

var a = new MySingletonClass();
var b = MySingletonClass();
console.log( a === b ); // prints: true

对于那些想要严格版本的人:

(function (global) {
  "use strict";
  var MySingletonClass = function () {

    if (MySingletonClass.prototype._singletonInstance) {
      return MySingletonClass.prototype._singletonInstance;
    }

    MySingletonClass.prototype._singletonInstance = this;

    this.Foo = function() {
      // ...
    };
  };

var a = new MySingletonClass();
var b = MySingletonClass();
global.result = a === b;

} (window));

console.log(result);

Answer 2

为什么要为单个对象使用构造函数和原型？

以上相当于:

var earth= {
    someMethod: function () {
        if (console && console.log)
            console.log('some method');                             
    }
};
privateFunction1();
privateFunction2();

return {
    Person: Constructors.Person,
    PlanetEarth: earth
};

Answer 3

通过Tom 扩展上述帖子,如果您需要类类型声明并使用变量访问单例实例,下面的代码可能会有所帮助.我喜欢这种符号,因为代码很少自我引导.

function SingletonClass(){
    if ( arguments.callee.instance )
        return arguments.callee.instance;
    arguments.callee.instance = this;
}


SingletonClass.getInstance = function() {
    var singletonClass = new SingletonClass();
    return singletonClass;
};

要访问单身人士,你会的

var singleTon = SingletonClass.getInstance();