function extend(subClass, superClass) {    var f = function() {};    f.prototype = superClass.prototype;    subClass.prototype = new f();    subClass.superClass = superClass.prototype;}var parent = function (name, age) {    this._name = name;    this._age = age;};parent.prototype.show = function () {    console.info(this._name + " : " + this._age);};var son = function(name,age,height) {    this._height  = height;    son.superClass.constructor.call(this,name,age);};extend(son, parent);//这里没有重写父类也就是parent的show方法son.prototype.show=function() {    console.info(this._name + " : " + this._age+" : "+this._height);};var s1 = new son("jack",12,120);s1.show();var p1 = new parent("father",40);p1.show();