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Featured topicLanguages & RuntimesIntermediate13 min
UPDATED OCT 7, 2026

Prototypes and Inheritance in JavaScript

How every object links to a prototype, how property lookup walks that chain, what new and class really do, and how prototype pollution turns it into a bug.

Diagrams · worked examples · interview questionsRead topic

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Languages & Runtimesinterview favoriteClosures and ScopeHow JavaScript resolves a variable, why a function keeps its birthplace alive, the loop puzzle, stale closures in React, and what closures cost in memory.Intermediate·13 minRead →Languages & Runtimesinterview favoritethis Binding in JavaScriptThe four call-site rules that decide what this is, why arrow functions ignore them, how methods lose this when passed around, and how to get it back.Intermediate·12 minRead →Languages & Runtimesinterview favoriteES Modules vs CommonJS: How JavaScript Modules LoadWhy require runs a file on the spot while import builds the whole graph first, what live bindings and circular imports do, and how Node picks a module system.Intermediate·14 minRead →Languages & Runtimesinterview favoriteGarbage Collection and Memory LeaksHow a garbage collector decides what is alive by tracing from roots, why generations and pauses matter for latency, and how JavaScript apps still leak memory.Intermediate·13 minRead →Frontend Architectureinterview favoriteMemoization in React: memo, useMemo, useCallbackWhy React re-renders a whole subtree, why a new object or function each render defeats React.memo, when memoizing pays off, and what the React Compiler changes.Intermediate·13 minRead →Frontend Architectureinterview favoriteReact Server ComponentsHow one React tree becomes two programs, what may cross the server/client boundary, why the payload is not HTML, and how streaming and server actions fit in.Intermediate·14 minRead →Frontend Architectureinterview favoriteState Management Trade-offs in Frontend AppsSort state by where it belongs before picking a library: server cache, URL, form, local UI or shared store, and why Context re-renders every consumer.Intermediate·14 minRead →Frontend Architectureinterview favoriteVirtual DOM and ReconciliationWhat the virtual DOM really is, how React diffs two trees in linear time, why keys decide which state survives, and how Fiber and signals change the picture.Intermediate·13 minRead →Frontend Architectureinterview favoriteHydration and Hydration ErrorsHow server HTML becomes an interactive app, why the first client render must match it exactly, what causes mismatches, and how to hydrate less.Intermediate·13 minRead →Frontend Architectureinterview favoriteOptimistic UI: Updating Before the Server AnswersShow the result of a click before the server confirms it, then reconcile or roll back. Which actions suit it, and how to survive races, refetches and retries.Intermediate·12 minRead →Frontend Architectureinterview favoriteWeb Accessibility FundamentalsHow the browser turns your DOM into the accessibility tree screen readers use, why semantic HTML beats ARIA, and how to get keyboard, focus and forms right.Intermediate·14 minRead →Web Performanceinterview favoriteThe Critical Rendering PathHow a browser turns HTML, CSS and JS into pixels, which resources block which step, and why some CSS changes cost a layout while others cost nothing.Intermediate·14 minRead →Web Performanceinterview favoriteCore Web VitalsWhat LCP, INP and CLS actually measure in the browser, the fixes that move each one, and why a green Lighthouse score can go with red field data.Intermediate·14 minRead →Web Performanceinterview favoriteHTTP CachingHow browsers and CDNs decide to reuse a response: freshness with Cache-Control, validation with ETag, cache keys with Vary, and the recipes that actually work.Intermediate·13 minRead →Web Performanceinterview favoriteImage Optimization: Formats, srcset and PriorityPick the format, let srcset and sizes choose the pixels for each screen, and load the hero first without layout shift: the three decisions behind fast images.Intermediate·13 minRead →Web Performanceinterview favoriteTree Shaking, Code Splitting and Bundle SizeWhy JavaScript bytes cost more than image bytes, how bundlers drop unused exports, what quietly stops them, and how splitting and budgets keep bundles small.Intermediate·13 minRead →Concurrency & Asyncinterview favoriteThe Event Loop: Microtasks vs MacrotasksHow JavaScript runs async code on a single thread, why promise callbacks beat setTimeout, and how to predict the output of any ordering puzzle.Intermediate·12 minRead →Concurrency & Asyncinterview favoriteWeb Workers: Getting Work Off the Main ThreadWhy one long JavaScript task freezes input, when yielding is enough, and how workers, transferables and SharedArrayBuffer move heavy work off the main thread.Intermediate·13 minRead →Networking & Protocolsinterview favoriteDNS Resolution: From Name to IP AddressHow a resolver walks root, TLD and authoritative servers to turn a name into an address, why TTL caching explains "propagation", and where DNS breaks.Intermediate·13 minRead →Networking & Protocolsinterview favoriteLoad Balancing: L4 vs L7, Algorithms, Health ChecksWhat L4 and L7 balancers actually forward, why least-request beats round robin, how health checks and draining make deploys safe, and why gRPC breaks it.Intermediate·13 minRead →
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Cheat sheets and interview prep for 461+ technologies

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Database

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