Patterns for solving common problems and needs. For example, what are the typical/recommended ways of solving authentication, data persistence, server rendering, etc.
Theory of design, use of color and creating color palettes, typography, UI/UX design and refactoring, etc.
HTML elements and attributes, Web APIs, CSS layout and positioning, animations, typography, basics of authoring and using SVG in webpages, CSS-in-JS frameworks (Emotion and Styled Components), all there is to know about React.
Node.js, web protocols (HTTP...), linked data and semantic web, REST APIs, GraphQL, database technologies, containers, hosting, UNIX.
Version control with git, command line (git commands, fish shell, tmux, nnn...) code editors (VS Code, Emacs, Vim), browser developer tools, debugging, graphics and design tools (GIMP, Inkscape, Figma...), testing, deployment and continuous integration (Jest, CircleCI, Webpack and Parcel, Now, Neflify...)