I have never been a really good JavaScript developer and generally I'm more a backend-oriented type of developer. But I recently decided to change that fact and do a lot more frontend stuff. To help me gain the necessary knowledge, I found JS-assessment developed by Rebecca Murphy to be very helpful.

JS-assessment is a test-driven approach to learn the basics and also some more advanced best practices in JavaScript. You can get it from Github. It runs a small HTTP server on node.js that you will use to run the tests.

All you have to do now is to write some small lines of code, so that the tests will run successfully and show green. The approach will also work perfectly as a coding dojo kata. Repeat it regularly and track your progress.