Low-Level Design
Design below the service line — the classes, interfaces and state machines behind one box.
5 topics
Object-Oriented Design in an Interview
Getting from a prose problem statement to classes and responsibilities in twenty minutes, without reciting design patterns.
core20 minDesigning a Class API
What makes an interface pleasant to use and hard to misuse — naming, argument shape, error handling, and the versioning consequences of every public method.
core20 minState Machines & Lifecycle Modelling
Replacing a scatter of booleans with an explicit set of states and legal transitions — the cheapest correctness win in most codebases.
core20 minConcurrency in Low-Level Design
Designing a component several things touch at once — what to make immutable, what to lock, and why the answer in JavaScript is different.
deep20 minLow-Level Design Classics
The recurring module-design prompts — an LRU cache, a rate limiter, a parking lot, a scheduler — and the one idea each is really testing.
core20 min