JavaScript, browser internals, React core, and CSS layout. The essential competence bar every frontend engineer needs before advancing to system design or DSA.
Closures, async, prototypes, event loop.
Rendering pipeline, memory, V8.
Hooks, Fiber, reconciliation, hydration.
Flexbox, grid, specificity, animations.
Types, generics, utility types.
Unit, integration, RTL, mocking.