Importing External Files in JavaScript

As JavaScript application grows, navigation on the code becomes a hell. It comes on mind how useful would be to have ability including JavaScript files. For example, thanks to include/require statements we can build an expressive file structure in PHP. Let’s say following PSR-0 standard we have one class per file (or one prototype object per file in JavaScript) and class name (namespace) reflects the location of the file where it belongs. Well, on server side (e.g. with NodeJS) that is achievable with CommonJS. Of course you have to export every object of a single file as a module, which is often not a module in fact. As for the client side, modular JavaScript implies that all the dependent modules load asynchronously and separately. If every object makes a module to load that sounds nothing like a good idea.