Using the original metaphor of a software sketchbook, p5.js has a full set of drawing functionality. However, you're not limited to your drawing canvas, you can think of your whole browser page as your sketch! For this, p5.js has addon libraries that make it easy to interact with other HTML5 objects, including text, input, video, webcam, and sound.
The library follows some of the same philosophy as Processing — that is, straightforward to get up and running — and reimagines the implementation and approach for recent web technology. Even if you're not into programming, it's worth visiting if just to watch, listen, and interact with Dan Shiffman as he enthusiastically talks about the library.