Functions ARE Objects!

Javascript is a functional, object-oriented language - but what exactly does that mean to you a developer? It means that functions ARE objects. You can add members to functions just as you could any object. Take for example, the following function that keeps track of how many times it's been called:

function count_times() {
 count_times.call_count = (count_times.call_count || 0) + 1;
 print(count_times.call_count);
}

Trivial example I know, but let your imagination go wild.

arguments.callee

Javascript Tip: Ever wonder what arguments.callee is for? Well, it contains the function being evaluated, so you can write anonymous recursive functions like the following:

(function(n) {
  if (n > 1)
     return n * arguments.callee(n-1);
  else
     return 1;
})(5);

Which is the same as the following written in a more traditional way:

function fact(n) {
   if (n > 1)
      return n * fact(n-1);
   else
      return 1;
}

fact(5);