Reading the landscape: what the ground is telling you
Landforms keep a record of what made them: a U-shaped valley, a line of springs along a cliff, rock layers meeting at an angle. Each question shows a photo of real terrain and...
Quizzes
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Real-time delivery: polling → SSE → WebSockets
"Make it real-time" hides a ladder of escalating tradeoffs. Climb it: short polling, long polling, Server-Sent Events, and WebSockets — when each is the right tool, how the...
Real-time over HTTP/2 & HTTP/3: multiplexing, QUIC & WebSocket bootstrapping
How HTTP/2 multiplexing, HTTP/3 over QUIC, and Extended CONNECT (RFC 8441/9220) reshape real-time delivery: application- vs transport-level head-of-line blocking, QUIC's...
Road signs around the world
Red rings, blue discs, upside-down triangles: road signs are a picture language shared by the 75 countries that have joined the 1968 Vienna Convention on Road Signs and...
Scaling WebSockets: sticky sessions, fan-out & backpressure
Running real-time WebSockets across a fleet: why connections need sticky sessions, how a pub/sub backplane fans messages across nodes, tracking presence, per-connection...
Server-sent events deep dive: the event stream format
The precise SSE wire format from the WHATWG HTML spec: comment/keep-alive lines, multi-line data, the dispatch rule, named vs default events, the id and retry fields, stopping...
Sociology of queues: waiting lines as social systems
Thirty-eight questions about waiting lines as social systems: first-come-first-served as a social contract, single serpentine queues, perceived waiting time, priority queues,...
SQL query detective
Read each query, predict what it returns, and spot the bug when the result is wrong. You'll work through joins, fan-out, NULL, aggregation, and filters that don't do what they...
Stateless Node.js services: workers, shared state, and graceful shutdown
A Node process runs your JavaScript on a single event-loop thread, so using more cores and more machines means changing how the service is built. Each Question covers one...
Systems-level CS in the browser: a frontend engineer's guide to reconciliation, the event loop, race conditions & hashing
A 40-question deep dive built to help frontend engineers better understand algorithms by grounding classic computer-science ideas in browser behavior you can actually observe....
Tabs, spaces and Vim: developer holy wars, measured
Developers have argued about tabs versus spaces and Vim versus Emacs for decades, and now and then someone collects data. Each Question takes one argument, shows what a survey,...
Tech mascots: where the penguin, the Octocat and the gopher came from
Linux has a penguin, GitHub has a cat with octopus arms, Go has a gopher, and Firefox is named after an animal that isn't in its logo. Each Question asks where a mascot came...