Basics of HTML & CSS, Inheritence rules, usage of selectors, media-queries, keyframes, bootstrap, creating and using npm packages, using ExpressJS for creating servers, handlebars for rendering in case of JS disabled pages and jQuery for making AJAX calls in case of JS enabled pages, MySQL for data persistence, Sequelize for ORM (Object Relational Mapping), REST APIs, Socket.IO for real-time messaging, MongoDB and mongoose for using NoSQL database, Authentication using PassportJS, Using Python scripts on NodeJS and running custom sklearn, tensorflow or keras pre-trained model in our backend.