JavaScript : Object-Oriented Programming

Functions are data

Functions in JavaScript are actually data. This is an important concept that we'll need later on. This means that you can create a function and assign it to a variable:

var f = function () {
  return 1;
};

This way of defining a function is sometimes referred to as function literal notation.

The part function () { return 1; } is a function expression. A function expression can optionally have a name, in which case it becomes a named function expression (NFE). So, this is also allowed, although rarely seen in practice (and causes IE to mistakenly create two variables in the enclosing scope: f and myFunc):

var f = function myFunc() {
  return 1;
};

As you can see, there's no difference between a named function expression and a function ...