I've decided to, as an educational exercise, implement DEFLATE compression / decompression and zip file format, and eventually tackling Excel format (which is just a .zip) so I can generate true excel spreadsheets (instead of .csv files) client-side using JavaScript.

Are there already libraries that do this? Yes, but then I don't get to try to implement these interesting algorithms. Is it currently 1 AM? Yes. Do I have work tomorrow? Also yes.

If I don't just fall flat on my face, I'll post updates!