qr.js: QR code generator in pure Javascript (2011)

This is a fairly standalone script for producing QR code on the fly.
Originally developed for my own interest, the code is fully commented and well-structured.
The code is in the public domain (or to be exact, Creative Commons Zero),
and you can use it for absolutely any purpose.

See also a node.js module based on qr.js, packaged by Nadav Ivgi.