xhr, promises, a modern build tool (webpack? browserify?), prototypal inheritance, virtual dom, object oriented programming, when to add more abstractions and w

xhr, promises, a modern build tool (webpack? browserify?), prototypal inheritance, virtual dom, object oriented programming, when to add more abstractions and when to tear them down, front-end performance & memory profiling, browser dev tools, canvas, svg, service workers, browser caching, cookies, websockets, SASS, Ecmascript 6, API design principles, data modeling, when to use a hash and when to use an array, basic concepts of UX, and of course, most importantly, box shadows