Constructor function return is other than “[Object object]”

问题

When I use the String constructor I allways wonder how is it made.It returns the string you specificed as a parameter even though it is instanciated with the "new" operator like :

  var str = new String("Hello World")
  //str == "Hello World"

If I make a constructor and I give it a return value it returns an Object when instanciated :

  function CreateString(st) {
  return ''+st 
  }
  var MyString = new CreateString("Hello there!")
  //MyString == "[Object object]"

How can I create a constructor that returns a value Other than [Object object] ?

Update: I am trying to create a constructor function that has both properties and a value itself like :

   function MyConstructor() {
    this.myMethod = function() {
     return 73
    }
     return 25
   }
    /*I want MyConstructor to have the value 25 and the myMethod method */
   alert(MyConstructor()) // to be 25
   alert(MyConstructor().myMethod()) //to be 73

回答1:

You can replace toString() function definition in the desired class.

function CreateString() {
  function toString() { return 'foo' }
}

Example: Number.prototype.toString()

回答2:

By this line

var MyString = new CreateString("Hello there!")

you're not simply calling function CreateString, you're creating a new Object of 'type' CreateString (an instance of a function).

I guess what you want is just

var MyString = CreateString("Hello there!")

来源：https://stackoverflow.com/questions/41808464/constructor-function-return-is-other-than-object-object