Buy the book! Can be purchased from The Pragmatic Bookshelf
Practice! These are language agnostic, progressively more challenging problems that were designed to be done in order. They have constraints and stretch goals to push the solver into exercising different programming techniques, and exploring features of whatever languages they use.
Each numbered directory contains language specific subdirectories with solutions in their respective language.
The Python solutions, thus far, don't use third-party libraries, so you should be able to easily run them locally if you have Python installed. Alternatively, here is an online REPL for Python. For the JavaScript solutions, copy and paste into your web browser's console.
The most mature solutions are in Python. I'll add more solutions and improve upon earlier ones as time permits.