Let's play with audio in Javascript by building a synthesizer for game sound effects (relatively short, potentially atonal sounds).
There are two potential back-ends for this system: the Audio object (<audio> tag), and the Web Audio API.
Understand these two different back-ends.
A good starting point might be the links in the Reference Material section below; though feel free to just start googling.
Your synth should work in chrome. There should be a clearly documented way to trigger a sound, and there should be some adjustable parameters that modify the sound. These parameters could be connected to a UI or simply be well-documented variables in the source code.