function fun(){
  var n=0;
  this.plus = function(){
      return n+=1;
  }  
}

var _fun = new fun();
console.log(_fun.plus())
console.log(_fun.plus())
console.log(_fun.plus())

// 第一种
function add1(){
    this.counter = 0;
}
// 在Javascript中每个函数都有一个Portotype属性，而对象没有，这个我们后面用面向对象再来解释
add1.prototype.plus=function(){
    return this.counter+=1;
}
var _add1 = new add1();
console.log(_add1.plus())
console.log(_add1.plus())

// 第二种
var add2 = function(){
    var obj = {};
    obj.counter = 10;
    obj.plus = function(){
        return this.counter+=1;
    }
    return obj;
}
var _add2 = new add2();
console.log(_add2.plus())
console.log(_add2.plus())

// 第三种
var add3 = new Function("this.counter = 20;this.plus = function(){return this.counter+=1;}");
var _add3 = new add3();
console.log(_add3.plus())
console.log(_add3.plus())

// 第四种
var add4={
    "counter":30,
    "plus":function(){
        return this.counter +=1;
    }
}
console.log(add4.plus())
console.log(add4.plus())

// 第五种 自调用函数
var add5 = (function(){
    var counter = 40;
    return function(){
        return counter += 1;
    }
})()
console.log(add5())
console.log(add5())

var obj = function(){
        
};
obj .show = function(){
    alert("我是静态方法");
};
obj .prototype.display = function(){
    alert("我是实例方法");
};
obj.display(); // obj.Display is not a function
obj.show(); //正确

var _obj = new obj();
_obj.display(); //正确
_obj.show(); //_obj.Show is not a function

var dom = function(){
        var Name = "Default";
        this.Sex = "Boy";
        this.success = function(){
            alert("Success");
        };
    };

    alert(dom.Name); // Undefined

    alert(dom.Sex); //Undefined

// 闭包
var person = (function(){
    var name="default"; //变量作用域为函数内部，外部无法访问
    return {
        getName:function(){
            return name;
        },
        setName:function(_name){
            name=_name;
        }
    }
})()

console.log(person.name)
console.log(person.getName())
person.setName("jhone")
console.log(person.getName())

// 顺便写个继承吧
var boy = function(){}
boy.prototype = person;
boy.prototype.say = function(){
	console.log("my name is " + this.getName());
}
var _boy = new boy();
_boy.setName("jack")
_boy.say();

// 只读属性 set get 是es5的中对象的特性
obj = {
    get x() {return 6},
    get y() {return 7}
};
console.log(obj.x)
console.log(obj.y)

obj = {};
Object.defineProperty(obj, "x", {value:4, writable:false}); //只读属性
console.log(obj.x)

// 使用闭包实现
var fun = (function(){
    var age = 27;
    return function(){
        return age;
    }
})();
console.log(fun())