This year, I have learned so much as a web developer that I cannot completely make the list.
Last year, I knew mostly Node.Js (and I had barely started to scratch the surface) so I knew barely anything in front-end. This year, after having learned of GIS development (ArcGiS API, Leaflet), I learned ReactJS, Webpack, SCSS, many design patterns and best practices, ...
I feel like a new person, and I am excited by the idea of everything I could learn in 2020.

And you ? What skills have you learned this year ?