Like Processing p5.js has the goal of making coding accessible for artists, designers, educators, and beginners. It provides users with facilities that can be summed up as "Programming for the Arts". In particular, it makes it easy to draw shapes, to add mouse interaction to your drawings and to generate sound.
These features are demonstrated in the Hello p5.js video by Daniel Shiffman, who may already be a familiar face from his Hello Processing video produced for last year's Hour of Code.
(click to run the video, you will need to use a browser that fully supports WebGL)
This isn't just a video you watch and listen to - it is one you interact with. The important point about it is that you are doing this in the browser and not on your desktop or an art installation, which is how you would be able to interact in a similar way with a program created in Processing.
p5.js is developed by artist and programmer Lauren McCarthy in collaboration with others including the students and faculty of the p5.js working group at the Interactive Telecommunications Program of New York University's Tisch School of Arts where Dan Shiffman is an Assistant Arts professor and Lauren McCarthy is a researcher in residence.
p5.js is in active development on GitHub and an official editing environment is billed as "coming soon" together with "many more features".