js继承

一、原型链继承

    function Parent(name) {
        this.name = name
        this.frineds = []
    }
    Parent.prototype.eating = function () {
        console.log(this.name + 'eating')
    }

    function Child(age) {
        this.age = age
    }
    Child.prototype.running = function () {
        console.log('running')
    }
    Child.prototype = new Parent()
    let obj = new Child(12)
    obj.frineds.push(123)
    let obj2 = new Child(11)
    console.log(obj.eating())
    console.log(obj.frineds, obj2.frineds)
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缺点：

1. 无法给继承属性赋值
2. 修改父元素的引用属性可能会影响其他对象的该引用属性
3. 子对象无法查看继承属性

二、构造继承

    function Parent(name) {
        this.name = name
        this.frineds = []
    }
    Parent.prototype.eating = function () {
        console.log(this.name + 'eating')
    }

    function Child(age, name) {
        Parent.call(this, name)
        this.age = age
    }
    Child.prototype = new Parent()
    Child.prototype.running = function () {
        console.log('running')
    }
    let obj = new Child(12, 'a')
    obj.frineds.push(123)
    let obj2 = new Child(11, 'b')
    console.log(obj.eating())
    console.log(obj.frineds, obj2.frineds)
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优点：解决了原型链继承的三个缺点 缺点：

1. 父构造函数调用了两次
2. 会多生成一份继承属性实例

三、寄生式继承

    let parentObj = {
        running: function () {
            console.log('running')
        }
    }
    function createChild(name) {
        let child = Object.create(parentObj)
        child.name = name
        return child
    }
    let child1 = createChild('aa')
    child1.running()
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四、寄生组合继承

    function Parent(name) {
        this.name = name
    }
    Parent.prototype.eating = function () {
        console.log(this.name + ' eating')
    }

    function Child(age, name) {
        Parent.call(this, name)
        this.age = age
    }
    inheritPrototype(Child, Parent)
    function inheritPrototype(SubType, SuperType) {
        SubType.prototype = Object.create(SuperType.prototype)
        Object.defineProperty(SubType.prototype, "constructor", {
            enumerable: false,
            configurable: true,
            writable: true,
            value: SubType
        })
    }
    Child.prototype.running = function () {
        console.log('running')
    }
    let obj = new Child(12, 'aaaa')
    console.log(obj.eating())
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