JavaScript new return 类的实例化

new初始化方法

简单没有return的就不写了

    function Person() {
         this.name="hongda";
         this.age=28;
          return "fffffff";
        }
        var p = new Person();
        console.dir(p);
        console.log(typeof p);
        var pp=Person();
        console.log(pp);
        console.log(typeof pp);

     function Person() {
         this.name="hongda";
         this.age=28;
          return new String("fffff");
        }
        var p = new Person();
        console.dir(p);
        console.log(typeof p);
        var pp=Person();
        console.log(pp);
        console.log(typeof pp);

从上面可以发现，如果返回的类型是object时，那么构造函数初始化返回的就是return返回的object

如果return返回的不是object时，那么就返回函数内部初始化的。

 function中有prototype情况

 function Person() {
         this.name="hongda";
         this.age=28;
         return "fffff";
        }
        Person.prototype={
          school:"nanjing",
          say:function(){}
        }
        
        var p = new Person();
        console.dir(p);
        console.log(typeof p);
        var pp=Person();
        console.log(pp);
        console.log(typeof pp);

function Person() {
         this.name="hongda";
         this.age=28;
         return new String("ffffff");
        }
        Person.prototype={
          school:"nanjing",
          say:function(){}
        }
        
        var p = new Person();
        console.dir(p);
        console.log(typeof p);
        var pp=Person();
        console.log(pp);
        console.log(typeof pp);

可以发现如果初始化返回的就是return返回的对象时，该初始化对象并不能获取prototype

反之就可以获取prototype.

特殊情况： 

Function：

 function Fun(){
 this.a="a";
 this.b="b";
 }
function Person() {
   this.name="hongda";
   this.age=28;
    return Fun;
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

function Person() {
   this.name="hongda";
   this.age=28;
    return new Function("var a='a';var b='b';");
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

Date：

function Person() {
   this.name="hongda";
   this.age=28;
    return new Date(22222222222222);
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

Object:

 function Fun(){
 this.a="a";
 this.b="b";
 }
function Person() {
   this.name="hongda";
   this.age=28;
    return new Fun();
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

Boolean:

function Person() {
   this.name="hongda";
   this.age=28;
    return true;
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

function Person() {
   this.name="hongda";
   this.age=28;
    return new Boolean(true);
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

Array:

 var arr=new Array(5);
 for(var i=0;i<5;i++){
  arr[i]=i;
 }
function Person() {
   this.name="hongda";
   this.age=28;
    return arr;
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

function Person() {
   this.name="hongda";
   this.age=28;
    return [1,2,3,4,5];
  }
  Person.prototype={
    school:"nanjing",
    say:function(){}
  }
  var p = new Person();
  console.dir(p);
  console.log(p.toString());
  console.log(typeof p);
  var pp=Person();
  console.log(pp);
  console.log(typeof pp);

 

还有一些特殊的情况

 var arr=new Array(5);
 for(var i=0;i<5;i++){
  arr[i]=i;
 }
 console.log(typeof arr);
 
 var list=[1,2,3,4,5];
 console.log(typeof list);
 
  var re = new RegExp("d(b+)(d)","ig");
  console.log(typeof re);
  
  var reg=/aw+/g;
  console.log(typeof reg);

全部都是object

var fun=function(){}
console.log(typeof fun);
var fun2=new Function("var a='hong';var b=24;");
console.log(fun2);
console.log(typeof fun2);

结论：返回的是Object类型或者function类型的，那么就返回return返回的，反之则返回实例化对象，同样适用于Boolean.