JavaScript中的构造函数总结

function fn(a) {

                this.a = a

                this.b = 20

                for (var i = 0; i < 10; i++) {

                    // console.log(i)

                }

                return "hello";

            }

            var re = new fn

            console.log(re)

这里函数的返回值是一个基本数据--字符串

所以他返回的是函数运行完的对象

function fn() {

                this.name = "karen"

                return function fm() {

                    console.log("fm运行了")

                    this.name = "jack"

                }

            }

            var f1=new fn()

            // f1

            //1.{}

            //2.{}.fn()里面的this是这个空对象==> {name:"Karen"}

            //3.f1=为fn函数返回值是不是引用数据 是就是它  不是就是那个创建的对象

            console.log(f1.name)//"fm"

var f2=new (new fn())()

这个就是要先看优先级 比较new无参和new带参的优先级谁更好然后是自调用 这个我们后面在细讲

然后做一个综合练习

// function fn() {

   //              this.name="marry"

            //  var obj = {

            //      name:"karen",

            //      fm: function() {

            //          this.name="jack"

            //      }

            //  }

            //  return obj;             

            // }

            

            // var f1=new fn()//{name:"marry"} f1=obj=>{name:"karen",fm:}

            // console.log(f1.name)//karen

            // var f2=new ((new fn()).fm) ()

            // console.log(f2.name)//jack           

            

            // var f3=new fn()

            // var f4=new (f3.fm) ()//{name:"jack"}

            // console.log(f3.name,f4.name)//karen,jack