Find a file/folder within another folder with OSX UI
Since you tagged this with “quicksilver”…

In Quicksilver, assuming all the project folders are in your catalog (which is easy to accomplish), you could type something like ca/mc↩ to open clientA/myCode.js.

Specifically, create a custom catalog entry that scans the parent folder containing your projects, or if they’re spread all over the place, you could tag them and add them to the catalog based on that, or list their paths in a file and scan that, or… There are a few options. :-)

Once they’re in the catalog, you can type the entire folder name (like clientA) if you hate yourself, but really, just type the first thing that comes to mind as fast as you can think it and Quicksilver will find it (like clta or ca). After doing this one or two times, it will become the top result.

With any folder selected, you can hit / or → to get at its contents. (For this reason, it’s unnecessary to have your catalog entries scan deep into the contents, but that’s an option if you want.)