单例模式

单例模式是指每一个类只会生成一个实例，这样可以节省开销，也容易进行业务管理，首先以TS来一段单例实现

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class Scene{
    public name:string;
    private static instance:Scene; 
    private constructor(name:string){
        this.name = name;
    }

    public static getInstance():Scene{
        if(!Scene.instance){
            Scene.instance = new Scene("Jonny");
        }
        return Scene.instance;
    }

}

//let a = new Scene("jonny"); //编译错误
let a = Scene.getInstance();
let b = Scene.getInstance();

console.log(a===b);   //true

再来看一下ES5实现

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function Scene(){
    this.name = 'jonny';
}

Scene.instance = null;

Scene.prototype.getName = function (){
    return Scene.instance.name;
}

Scene.getInstance = function (){
    if(!Scene.instance){
       Scene.instance = new Scene(); 
    }
    return Scene.instance;
}

var a = Scene.getInstance();
var b = Scene.getInstance();
console.log(a===b); //true
console.log(a.getName()); //'jonny'