javascript object-oriented, constructor

   在微信公众号“前端大全”中看到了波同学的讲解面向对象、构造函数、原型与原型链等内容，之前对于这几个知识点有去理解与使用过，但大多是处于似懂非懂的阶段，会用而已。今天凑巧看到了波同学的讲解，就此记录。

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Object definition

An unordered collection of attributes, whose attributes can contain basic values, objects, or functions. It consists of a series of unordered key-value pairs in javascript

    //对象
    var person = {
        name: 'Tom',//基本值
        age: 18,
        getName: function() {
    
    },//函数
        parent: {}//对象
    }
    //创建对象
    var obj=new Object();
    var obj={};
    //给创建的对象添加方法
    var person={}；
    person.name="mon"；
    person.getName=function(){
    
    
        return this.name;
    }
    var person={
        name:"mon",
        getName:function(){
    
    
            return this.name;   
        }
    }
    //访问对象的属性和方法
    person.name
    person['name']
    ['name','age'].forEach(funciton(item){
        console.log(person[item]);
    })

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Factory mode

Provide a model, and then copy the object we need through this model

    var createPerson=function(name,age){
    
    
    //声明一个中间对象，该对象就是工厂模式的模子
        var o=new Object();
        //依次添加我们需要的属性和方法
        o.name=name;
        o.age=age;
        o.getName=function(){
    
    
            return this.name;
        }
        return o;   
    }
    //创建两个实例
    var perTom=createPerson('Tom',20);
    var perJake=createPerson('Jake',22);
    //识别对象实例的类型
    var obj={};
    var foo=function(){
    
    };
    console.log(obj instanceof Object);//true
    console.log(foo instanceof Function);//true

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Constructor

1. Compared with ordinary functions, there is nothing special about constructors. The capitalization of the first letter is just a small convention to distinguish ordinary functions.
2. The new keyword makes the constructor have many characteristics different from ordinary functions. The process is as follows: ①Declare
an intermediate object ②Point
the prototype of the intermediate object to the prototype of
the constructor ③Point the this of the constructor to the intermediate object
④ Return the intermediate object, that is, return the instance object

    //创建构造函数
    var Person=function(name,age){
    
    
        this.name=name;
        this.age=age;
        this.getName=function(){
    
    
            return this.name;
        }
    }
    //将构造函数以参数形式传入
    function New(func){
    
    
        //声明一个中间对象，该对象为最终返回的实例
        var res={}；
        if（func.prototype!==null）{
            //将实例的原型指向构造函数的原型
            res._proto_=func.prototype;
        }
        //ret为构造函数执行的结果，通过apply，将构造函数内部的this指向修改为指向res，即为实例对象
        var ret=func.apply(res,Array.prototype.slice.call(arguments,1));
        //当我们在构造函数中明确指定了返回对象时，那么new的执行结果就是该返回对象
        if((type ret==="object"||typeof ret==="function")&&ret !=null){
            return ret;
        }
        //如果没有明确指定返回对象，则默认返回res，这个res就是实例对象
        return res;
    }
    //通过new声明创建实例
    var p1=New(Person,'tom',20);//p1实际接收的是new返回的res,等效于var p1=new Person('tom',20);
    console.log(p1.getName());
    console.log(p1 instanceof Person);//true