Learn to create gorgeous web pages and captivate audiences with HTML5 and CSS3. Often introduced but rarely mastered, HTML & CSS have more depth than you may imagine.
Database & Modeling
Relational and document databases are two of the prevailing paradigms used today. Every full-stack web developer should be comfortable with SQL, object-stores, and properly modeling a database.
Testing code manually becomes tedious and the effort is proportional to the complexity of the app. For source code to be considered maintainable it must have automated tests and for this reason you must learn about the tools, methodologies and best practices, including Test-driven Development.
React is a UI library developed at Facebook to facilitate the creation of interactive, stateful & reusable UI components. It is used at Facebook in production, and Instagram.com is written entirely in React.