Why in JavaScript is a function considered both a constructor and an object?

Question

I have been doing a lot of research on this lately, but have yet to get a really good solid answer. I read somewhere that a new Function() object is created when the JavaScr

Answer 1

Your understanding is wrong:

myFunction().myProperty; // myFunction has no properties

The reason it does not work is because ".myProperty" is applied to the returned value of "myFunction()", not to the object "myFunction". To wit:

$ js
js> function a() { this.b=1;return {b: 2};}
js> a().b
2
js> 

Remember, "()" is an operator. "myFunction" is not the same as "myFunction()". You don't need a "return" when instanciang with new:

js> function a() { this.b=1;}
js> d = new a();
[object Object]
js> d.b;
1

Answer 2

Indeed, Functions are 'first class citizens': they are an Object.

Every object has a Prototype, but only a function's prototype can be referenced directly. When new is called with a function object as argument, a new object is constructed using the function object's prototype as prototype, and this is set to the new object before the function is entered.

So you could call every function a Constructor, even if it leaves this alone.

There are very good tutorials out there on constructors, prototypes etc... Personally I learned a lot from Object Oriented Programming in JavaScript. It shows the equivalence of a function which 'inherits' its prototype, but uses this to fill in a new object's properties, and a function object that uses a specific prototype:

function newA() { this.prop1 = "one"; } // constructs a function object called newA
function newA_Too() {} // constructs a function object called newA_Too
newA_Too.prototype.prop1 = "one";

var A1 = new newA();
var A2 = new newA_Too();
// here A1 equals A2.