Creating basic javascript library structure [on hold]

I'm interested in creating a basic javascript library structure ( structure because a library is a broad subject ). I looked at the jquery code for inspiration but there are things I don't understand.

Here is an example of what I don't understand:

(function( global, factory ) {
if ( typeof module === "object" && typeof module.exports === "object" ) {
    module.exports = global.document ?
        factory( global, true ) :
        function( w ) {
            if ( !w.document ) {
                throw new Error( "jQuery requires a window with a document" );
            }
            return factory( w );
        };
} else {
    factory( global );
}
}(typeof window !== "undefined" ? window : this, function( window, noGlobal ){ ... }

Question:

What is happening in the code above? And is this needed to create the structure of a javascript library?

Thank you.

i don't know i saw it in every js lib!