JavaScript面向对象编程--继承

继承

原型链

function SuperType() {
    this.property = true;
}
SuperType.prototype.getSuperValue = function() {
    return this.property;
};
function SubType() {
    this.subproperty = false;
}
// 继承了 SuperType
SubType.prototype = new SuperType();
SubType.prototype.getSubValue = function() {
    reurn this.subproperty;
}
var instance = new SubType();
alert(instance.getSuperValue());

原型链的问题

1. 最主要的问题来自包含引用类型值的原型；
2. 不能向超类的构造函数中传递参数。

借用构造函数

function SuperType() {
    this.colors = ["red", "bule", "green"];
}
function SubType() {
    // 继承了SuperType
    SuperType.call(this);
}
var instance1 = new SubType();

借用构造函数的问题

和构造函数模式存在一样的问题–无法实现方法复用。

组合继承

function SuperType(name) {
    this.name = name;
    this.colors = ["red", "bule", "green"];
}
SuperType.prototype.sayName = function() {
    alert(this.name);
};
function SubType(name, age) {
    // 继承属性
    SuperType.call(this, name);
    this.age = age;
}
// 继承方法
SubType.prototype = new SuperType();
SubType.prototype.constructor = SubType;
SubType.prototype.sayAge = function() {
    alert(this.age);
}
var instance1 = new SubType("Nicholas", 29);

原型式继承

function object(o) {
    function F(){}
    F.prototype = o;
    return new F();
}
var Person = {
    name: "Nicholas",
    friends: ["Shelby", "Court", "Van"]
};
var anotherPerson = object(person);

Object.create()方法规范化了原型式继承。

寄生式继承

function createAnother(original) {
    var clone = Object.create(original);
    clone.sayHi = function() {
        alert("hi");
    }
    return clone;
}
var person = {
    name: "Nicholas",
    friends: ["Shelby", "Court", "Van"]
}
var anoterPerson = createAnother(person);

寄生组合式继承

组合继承存在的问题：调用两次构造函数。寄生组合式继承就是解决这个问题的方案。

function inheritPrototype(subType, superType) {
    var prototype = Object.create(superType.prototype); // 创建对象
    prototype.constructor = subType; // 增强对象
    subType.prototype = prototype; // 指定对象
}
function SuperType(name) {
    this.name = name;
    this.colors = ["red", "bule", "green"];
}
SuperType.prototype.sayName = function() {
    alert(this.name);
};
function SubType(name, age) {
    // 继承属性
    SuperType.call(this, name);
    this.age = age;
}
inheritPrototype(SubType, SuperType);
SubType.prototype.sayAge = function() {
    alert(this.age);
}
var instance1 = new SubType("Nicholas", 29);