原型继承方法记录

// PrimaryStudent构造函数:function PrimaryStudent(props) {    Student.call(this, props);    this.grade = props.grade || 1;}// 空函数F:function F() {}// 把F的原型指向Student.prototype:F.prototype = Student.prototype;// 把PrimaryStudent的原型指向一个新的F对象，F对象的原型正好指向Student.prototype:PrimaryStudent.prototype = new F();// 把PrimaryStudent原型的构造函数修复为PrimaryStudent:PrimaryStudent.prototype.constructor = PrimaryStudent;// 继续在PrimaryStudent原型（就是new F()对象）上定义方法：PrimaryStudent.prototype.getGrade = function () {    return this.grade;};// 创建xiaoming:var xiaoming = new PrimaryStudent({    name: '小明',    grade: 2});xiaoming.name; // '小明'xiaoming.grade; // 2// 验证原型:xiaoming.__proto__ === PrimaryStudent.prototype; // truexiaoming.__proto__.__proto__ === Student.prototype; // true// 验证继承关系:xiaoming instanceof PrimaryStudent; // truexiaoming instanceof Student; // true

借助中间空函数实现
new PrimaryStudent() ----> PrimaryStudent.prototype ----> Object.prototype ----> null
到
new PrimaryStudent() ----> PrimaryStudent.prototype ----> Student.prototype ----> Object.prototype ----> null
的转变

还可以用封装函数inherits()，可以隐藏F的定义，并简化代码：

function inherits(Child, Parent) {    var F = function () {};    F.prototype = Parent.prototype;    Child.prototype = new F();    Child.prototype.constructor = Child;}