Function expression hoisting

Function expressions in JavaScript are not hoisted, unlike function declarations. You can't use function expressions before you declare them:

notHoisted(); // TypeError: notHoisted is not a function

var notHoisted = function() {
   console.log("bar");
};

Named function expression

If you want to refer to the current function inside the function body, you need to create a named function expression. This name is then local only to the function body (scope). This also avoids using the non-standard arguments.callee property.

var math = {
  'factorial': function factorial(n) {
    if (n <= 1)
      return 1;
    return n * factorial(n - 1);
  }
};