CORS: why is the browser blocking me?
Work through how browsers handle origins, CORS, preflights, credentials, opaque responses, SameSite cookies, CSP, CSRF, and the classic "but it works in Postman" trap.
Quizzes
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CSS cascade, specificity & inheritance
Read CSS conflicts the way the engine does: specificity by column, why @layer order outranks specificity (and how !important reverses it), unlayered-beats-layered, inherited...
CSS stacking contexts & z-index: real problems, real fixes
Why z-index: 9999 sometimes does nothing, what silently creates a stacking context, how the paint order actually works, and when isolation: isolate is the surgical fix. Every...
Dark patterns: confirmshaming, roach motels and preselected consent
Nineteen interfaces built to work against the person using them. Every question shows a design as a mockup and asks what it is doing; every explanation shows the same screen...
Data structures hiding in your codebase: a field guide for frontend engineers
Algorithms feel abstract until you spot them in the code you already ship. This quiz is for frontend engineers who want to understand algorithms by recognising the data...
Database isolation and consistency: CAP, isolation levels, and locking
CAP, isolation levels, and locking, as the docs and papers define them. Learn why partition tolerance is never optional, what PostgreSQL's default Read Committed lets through,...
Dates and times in JavaScript, Temporal, and PostgreSQL
How dates break in real code: local times that never happen, offsets that aren't time zones, instants versus wall-clock time, leap seconds, ISO 8601 traps, meetings that drift...
Debounce is a sliding window: algorithms for frontend engineers
You already ship algorithms, even if you've never called them that. These 50 questions connect five of them to code you write every day: stable sorting and locale-aware...
Debugging with distributed traces: waterfall shapes, context propagation & sampling
A distributed trace shows one request's path through every service it touched. Once you learn to read its shape, you can often spot the bug before you open a single log. This...
Docker in practice: build cache, image layers, stop signals & container storage
Each Question puts you in a concrete Docker situation. You decide what reaches the builder, when the build cache hits, what ends up in the image, how containers stop, how ports...
English for code reviews
Practical English for pull requests and code reviews, organized as a small curriculum: commit subjects and PR titles, PR descriptions, the grammar that trips up non-native...
Everyday economics: costs, incentives, and trade-offs
Thirty questions on the economics of everyday choices. You'll practice opportunity cost, sunk costs, marginal cost, fixed and variable costs, incentives that backfire, scarcity...