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

To answer your specific question, technically functions are always objects.

For instance, you can always do this:

function foo(){
  return 0;
}
foo.bar = 1;
alert(foo.bar); // shows "1"

Javascript functions behave somewhat like classes in other OOP languages when they make use of the this pointer. They can be instantiated as objects with the new keyword:

function Foo(){
  this.bar = 1;
}
var foo = new Foo();
alert(foo.bar); // shows "1"

Now this mapping from other OOP languages to Javascript will fail quickly. For instance, there is actually no such thing as classes in Javascript - objects use a prototype chain for inheritance instead.

if you're going to do any sort of significant programming in Javascript, I highly recommend Javascript: The Good Parts by Crockford, that guy you emailed.