Should I learn processing if I know D3.js?

Answer 1

Sure! If you want to, of course. It depends on what you need D3.js and Processing for exactly. If you only need to make data visualizations on the web, then D3 is more than sufficient to get the job done. If you're looking to work with Java and make interactive designs, then Processing is going to be necessary. And if you're looking for the modern JavaScript version of Processing then check out p5.js - this is how I started seriously learning JavaScript by the way.