Javascript 'this' keyword Inside a Nested Function

Question

This Javascript code is using the 'this' keyword inside a nested function (which is nested within a constructor):

o=new MyCtor();
for (var p in o) {
  print(p);
  print(o[p]);
}
function MyCtor() {
  this.a=1;
  var instance=this;
  nested();
  function nested() {
    this.b=2;
    instance.c=3;
  }
}

Result is this:

a
1
c
3

Note the print() just dumps the output to the screen like alert() in a browser (I'm testing with a standalone Spidermonkey, not inside a browser). Notice that property 'b' cannot be created by the 'this.b'.

Just wondering what is 'this' refering to in a nested function inside a constructor?

Answer 1

Since you are calling the function directly (not as an object property) and without the new keyword, this is the default object (window in a web browser, global in node, etc).

See a live demo on jsfiddle.

Answer 2

It refers to the Window. See for yourself by running this fiddle and opening the console: http://jsfiddle.net/sveinatle/9brLj/