What is define([ , function ]) in JavaScript?

That's probably a requireJS module definition

Check here for more details

RequireJS is a JavaScript file and module loader. It is optimized for in-browser use, but it can be used in other JavaScript environments, like Rhino and Node. Using a modular script loader like RequireJS will improve the speed and quality of your code.

define() is part of the AMD spec of js

See:

• https://github.com/amdjs/amdjs-api/wiki/AMD

Edit: Also see Claudio's answer below. Likely the more relevant explanation.