javascript实现单例模式

单例模式：多次实例化，最终也只有一个实例被创建，所有的方法和属性，都只能通过这个被创建的实例进行调用。

1.实现方式一：用一个变量来标志当前的类已经创建过对象

用一个变量来标志当前的类已经创建过对象，如果下次获取当前类的实例时，直接返回之前创建的对象即可

//通过一个变量来标识实例已经被创建，如果已经创建过实例就不再创建
function Singleton(name){
    this.name = name;
    this.instance = null;
}
 
Singleton.prototype.getName = function(name){
    console.log(name);
}
 
Singleton.getInstance = function(name){
   if(!this.instance) this.instance = new Singleton(name);
   return this.instance;
}
 
let a = Singleton.getInstance("a");
let b = Singleton.getInstance("b");
console.log(a === b);

2.实现方式二：闭包

function Singleton(name){
    this.name = name;
    this.instance = null;
}
 
Singleton.prototype.getName = function(name){
    console.log(name);
}
 
Singleton.getInstance = (function(name){
    return function(name){
        if(!this.instance) this.instance = new Singleton(name);
        return this.instance;
    }
})()
 
let a = Singleton.getInstance("a");
let b = Singleton.getInstance("b");
console.log(a === b);

3.实现方式三：闭包+构造函数

function CreateSingleton(name){
    this.name = name;
    this.getName(name);
}
 
CreateSingleton.prototype.getName = function(name){
    console.log(name);
}
 
const Singleton = (function(name){
    let instance = null;
    return function(name){
        if(!instance) instance = new CreateSingleton(name);
    return instance;
    }
})();
 
let a = new Singleton("a");
let b = new Singleton("b");
console.log(a === b);