js通过继承实现私有函数

function A(){
    this.x = 100;
    this.y = 200;
    this.f = function(){
        console.log(this.x + this.y);
    }
　　//私有函数
    this.g = function(){
        console.log(this.x - this.y);
    }
}

function C(){
    var a = new A();
    var o = new Object();
    o.x = a.x;
    o.y = a.y;
    o.f = a.f;
    return o;
}

function B(){

}

B.prototype = C();

function run(){
    var b = new B();
    b.f();
}