Question

I wasn’t sure how to ask this, and I apologize if it’s been asked already, but I could not find it or an answer.

What is returned when you assign a function to a var.

    var obj = function(){
        this.name = 'Steve';
    }
    alert( obj.name === '');//true
    obj.name = 'Mike';
    alert( obj.name === '');//true
    obj.foo = 'fall';
    alert( obj.foo );//fall

I know obj is now a function/object and I can call obj(). I also know that the function attached to obj is a constructor for new objects of type obj. If I do

var newObj = new obj();
alert( newObj.name );//Steve

“Steve” is printed. etc. etc.

Why does obj seem to have a property called “name” attached to it? And why when I try to assign a value to that property does it not get assigned?

Answer 1

Because function objects have aname property (which is non-standard by the way) that represents the “name” of the function, your function shows an empty string ("") as the value of this property because it’s anonymous.

For example, if you declare a function with the name foo:

function foo() {}
foo.name; // "foo"


var anon = function () {};
anon.name; // "", an anonymous function

var namedFunctionExpr = function bar () {};
namedFunctionExpr.name; // "bar"

Also as you noted, you can’t change the value of this property, since in most implementations, it’s non-configurable, non-enumerable and non-writable:

Object.getOwnPropertyDescriptor(function x(){}, 'name'); 
/* logs:
{ 
  configurable: false,
  enumerable: false,
  value: "x",
  writable: false
}
*/

Remember, this property is non-standard and there are some implementations that don’t support it (e.g. all IE JScript versions do not support it)

Now as @Felix suggest, I would like to add that this.name doesn’t have anything to do with your function’s name property.

In your example, calling the obj function as a constructor (with the new operator), sets the this value to a newly created object, that inherits from your function’s prototype, and you are assigning a value to the name property to this new object.