Processing is a programming language specialized for producing visual art. Its standard library includes functions for drawing 2D and 3D objects as well as taking user input.

P5.js is a JavaScript port of this standard library, allowing one to use similar syntax as Processing but in the context of a <canvas> element.

P5.js Web Editor is a web editor to allow one to create using P5.js without downloading anything. Therefore, this is more like Codepen, but for the specific purpose of creating visualizations and not normal webpages.