function syntax

I took over an ActionScript job.

While getting familiar with the style of coding used I came across some syntax I don't quite understand.

I could not find the answer in the forums.

Here is a snippet of code:

(function () {

var __this = {};

createjs.EventDispatcher.initialize(__this);

window.eventSource = __this;

})();

Is this declaring a function as a class?

We are publishing as Canvas/HTML5.

Thank you,

Mike