在Node.js版本6中工作:

class Foo {
  constructor(msg) {

    if (Foo.singleton) {
      return Foo.singleton;
    }

    this.msg = msg;
    Foo.singleton = this;
    return Foo.singleton;
  }
}

我们测试:

const f = new Foo('blah');
const d = new Foo('nope');
console.log(f); // => Foo { msg: 'blah' }
console.log(d); // => Foo { msg: 'blah' }

我反对我的回答，看看我的另一个。

通常，模块模式(参见Christian C. Salvadó的答案)不是单例模式就足够好了。然而，单例的一个特点是它的初始化会延迟到需要对象时。模块模式缺乏这个特性。

我的命题(CoffeeScript):

window.singleton = (initializer) ->
  instance = undefined
  () ->
    return instance unless instance is undefined
    instance = initializer()

在JavaScript中编译为:

window.singleton = function(initializer) {
    var instance;
    instance = void 0;
    return function() {
        if (instance !== void 0) {
            return instance;
        }
        return instance = initializer();
    };
};

然后我可以做以下事情:

window.iAmSingleton = singleton(function() {
    /* This function should create and initialize singleton. */
    alert("creating");
    return {property1: 'value1', property2: 'value2'};
});


alert(window.iAmSingleton().property2); // "creating" will pop up; then "value2" will pop up
alert(window.iAmSingleton().property2); // "value2" will pop up but "creating" will not
window.iAmSingleton().property2 = 'new value';
alert(window.iAmSingleton().property2); // "new value" will pop up

我从JavaScript模式中得到了这个例子 用编码和设计模式构建更好的应用程序一书(Stoyan Stefanov著)。如果你需要一些简单的实现类，比如单例对象，你可以使用一个直接函数，如下所示:

var ClassName;

(function() {
    var instance;
    ClassName = function ClassName() {
        // If the private instance variable is already initialized, return a reference
        if(instance) {
            return instance;
        }
        // If the instance is not created, save a pointer of the original reference
        // to the private instance variable.
        instance = this;

        // All constructor initialization will be here
        // i.e.:
        this.someProperty = 0;
        this.someMethod = function() {
            // Some action here
        };
    };
}());

你可以通过下面的测试用例来检查这个例子:

// Extending defined class like singleton object using the new prototype property
ClassName.prototype.nothing = true;
var obj_1 = new ClassName();

// Extending the defined class like a singleton object using the new prototype property
ClassName.prototype.everything = true;
var obj_2 = new ClassName();

// Testing makes these two objects point to the same instance
console.log(obj_1 === obj_2); // Result is true, and it points to the same instance object

// All prototype properties work
// no matter when they were defined
console.log(obj_1.nothing && obj_1.everything
            && obj_2.nothing && obj_2.everything); // Result true

// Values of properties which are defined inside of the constructor
console.log(obj_1.someProperty); // Outputs 0
console.log(obj_2.someProperty); // Outputs 0

// Changing property value
obj_1.someProperty = 1;

console.log(obj_1.someProperty); // Output 1
console.log(obj_2.someProperty); // Output 1

console.log(obj_1.constructor === ClassName); // Output true

这种方法通过了所有测试用例，而当使用原型扩展时，私有静态实现将失败(它可以被修复，但并不简单)，而公共静态实现则不太可取，因为实例是公开给公众的。

jsFiddly demo.

我的意见:我有一个构造函数(CF)，例如，

var A = function(arg1){
  this.arg1 = arg1
};

我只需要这个CF创建的每个对象都是相同的。

var X = function(){
  var instance = {};
  return function(){ return instance; }
}();

Test

var x1 = new X();
var x2 = new X();
console.log(x1 === x2)

我发现下面是最简单的单例模式，因为使用new操作符可以立即在函数中使用它，消除了返回对象字面量的需要:

Var singleton = new(函数(){ var private = "一个私有值"; 这一点。printSomething = function() { console.log(私人); ｝ }) (); singleton.printSomething ();

最明确的答案应该是Addy Osmani所著的《学习JavaScript设计模式》一书。

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 = "I'm 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; } }; })();