javascript学习笔记--经典继承、组合继承、原型式继承、寄生继承以及寄生组合继承

经典继承

js中实现经典继承的方式是通过构造函数来实现的，即在子类中对父类调用call方法。

  function Geometric() {
                this.time = "";
                this.color = "";
                this.base = function () {
                    alert("Creating time is: " + this.time + " and color is: " + this.color)
                }
            }
    
            function Circle() {
                Geometric.call(this);
                this.radius = 0;
                this.area = function () {
                    alert("the area is: " + Math.PI * this.radius * this.radius)
                    
                }
            }
            function Rectangle() {
                Geometric.call(this);
                this.wi = 0;
                this.he = 0;
                this.area = function () {
                    alert("the area is: " + this.wi * this.he)
                }
            }
            var instance1 = new Circle()
           
            instance1.time = "20xx.xx.xx"
            instance1.color = "red"
            instance1.radius = 0.3;
            instance1.area()
            instance1.base()
            
    
            var instance2 = new Rectangle()
            instance2.time = "20xx.xx.xx"
            instance2.color = "blue"
            instance2.wi = 3;
            instance2.he = 4;
            instance2.area();
            instance2.base();

　　

组合继承

组合继承又称伪经典继承，是通过原型链（实现对原型属性和方法的继承） +借用构造函数（实现对实例属性的继承） 。

父类的方法定义在父类的原型上；子类中继续进行父类的call方法的调用；让子类的原型指向父类；子类的方法定义在子类原型上。

  //组合继承
        //原型链+借用构造函数
        function Geometric() {
            this.time = "";
            this.color = "";

        }
        //方法定义在构造函数的原型上
        Geometric.prototype.base = function () {
            alert("Creating time is: " + this.time + " and color is: " + this.color)
        }

        function Circle() {
            Geometric.call(this);
            this.radius = 0;

        }
        Circle.prototype = new Geometric()
        Circle.prototype.area = function () {
            alert("the area is: " + Math.PI * this.radius * this.radius)
        }
        var instance3 = new Circle();
        instance3.time = "20xx.xx.xx"
        instance3.color = "green";
        instance3.radius = "20"
        instance3.base();
        instance3.area();

原型式继承

原型式继承使用了一个空函数对象F来作为原型链的中间变量。

父类的方法定义在父类的原型上；子类中继续进行父类call方法的调用；构造一个空函数对象F；让F的原型=父类的原型；子类的原型=F；子类原型的构造函数=子类；子类的方法构造在子类原型上。

  //原型式继承
        //使用一个空函数F来当做中间对象
        function Geometric() {
            this.time = "";
            this.color = "";

        }
        //方法定义在构造函数的原型上
        Geometric.prototype.base = function () {
            alert("Creating time is: " + this.time + " and color is: " + this.color)
        }
        function Circle() {
            Geometric.call(this);
            this.radius = 0;

        }

        function F() { }
        F.prototype = Geometric.prototype;
        Circle.prototype = new F()
        Circle.prototype.constructor = Circle();


        Circle.prototype.area = function () {
            alert("the area is: " + Math.PI * this.radius * this.radius)
        }

        var instance4 = new Circle();
        instance4.time = "2018.06.03"
        instance4.color = "green";
        instance4.radius = "20"
        instance4.base();
        instance4.area();
        alert(instance4.__proto__ == Circle.prototype)
        alert(instance4.__proto__.__proto__ == Geometric.prototype)

寄生继承

寄生继承了创建一个用于封装继承过程的函数。

创建一个继承函数；传入一个父类对象；在函数内构造该父类对象；在函数内创建子类；return该父类对象；

//寄生继承
        //创建一个用于封装继承过程的函数
        function createGeometric(g) {
            var clone1 = Object(g);
            clone1.createCircle = function (radius) {
                this.radius = radius;
                this.circleArea = function () {
                    alert("the area is: " + Math.PI * this.radius * this.radius)

                }
            }
            clone1.createRectangle = function (wi, he) {
                this.wi = wi;
                this.he = he;
                this.rectangleArea = function () {
                    alert("the area is: " + this.wi * this.he);
                }
            }
            clone1.base = function () {
                alert("Creating time is: " + g.time + " and color is: " + g.color)
            }
            //最后要将新创建的对象return出去
            return clone1
        }
        var g = {
            time: "20xx.xx.xx",
            color: "red"
        }


        var Geometric = createGeometric(g);

        Geometric.base();
        Geometric.createCircle(2.0);
        alert(Geometric.circleArea())
        Geometric.createRectangle(4, 5);
        alert(Geometric.rectangleArea())

寄生组合继承

寄生组合继承避免了组合继承中的一些冗余现象。

组合继承中：子类中进行了父类call方法的调用；子类的原型指向父类；这样就会有一定的冗余。

寄生组合继承中，通过一个函数（此处写为inheritPrototype）来代替子类的原型指向父类这一过程

    //寄生组合继承，避免了组合继承中的冗余现象
        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 Geometric() {
            this.time = "";
            this.color = "";

        }
        //方法定义在构造函数的原型上
        Geometric.prototype.base = function () {
            alert("Creating time is: " + this.time + " and color is: " + this.color)
        }

        function Circle() {
            Geometric.call(this);
            this.radius = 0;

        }
        //Circle.prototype = new Geometric()
        inheritPrototype(Circle, Geometric)
        Circle.prototype.area = function () {
            alert("the area is: " + Math.PI * this.radius * this.radius)
        }
        var instance5 = new Circle();
        instance5.time = "20xx.xx.xx"
        instance5.color = "green";
        instance5.radius = "20"
        instance5.base();
        instance5.area();