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Aporeon

Technical interview practice, from one developer to another.

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Debugging scenarioMedium~7 min

A method works when called directly but loses its receiver when passed as a callback. What happened?

Explains call-site-dependent this binding and compares wrapper, bind, and arrow-function fixes.

Debugging scenarioMedium~10 min

A page repeatedly reads and writes layout during interaction and becomes slow. How would you diagnose and fix it?

Diagnoses forced synchronous layout from interleaved geometry reads and style writes, then batches work and reduces its scope.

CSSHTMLJavaScript

Debugging scenarioMedium~10 min

A rejected promise bypasses the error handling you expected. How do errors propagate through promises and async/await?

Traces synchronous throws and promise rejections through chains, awaits, missing returns, and detached work.

Debugging scenarioMedium~10 min

A value is missing even though the TypeScript model appeared to allow the code. How would you model and narrow nullable or optional data correctly?

Separates optional, undefined, null, and invalid external data, then narrows values at the correct boundary.

JavaScriptTypeScript

Concept questionMedium~7 min

How does JavaScript's prototype model relate to class syntax?

Relates JavaScript classes to prototype-based delegation while preserving the useful semantics class syntax adds.

Concept questionMedium~7 min

How does the browser turn HTML and CSS into pixels, and which steps can block or repeat?

Explains DOM and CSSOM construction, style, layout, paint, and compositing as a practical performance model.

CSSHTMLJavaScript

Concept questionMedium~7 min

How do generics and constraints make a TypeScript API reusable without weakening its contract?

Uses generics to preserve relationships between types and constraints to express the operations an implementation requires.

JavaScriptTypeScript

Comparison questionEasy~5 min

How do var, let, and const differ in scope, initialization, and reassignment?

Compares JavaScript declarations through scope, initialization, redeclaration, reassignment, and practical default choices.

Comparison questionMedium~7 min

How do you choose between an interface and a type alias in production TypeScript?

Chooses interfaces or aliases based on object contracts, unions, composition, declaration merging, and team consistency.

JavaScriptTypeScript

Comparison questionMedium~10 min

How would you choose among cookies, localStorage, sessionStorage, and IndexedDB for browser data?

Chooses browser storage by server transport, lifetime, capacity, query needs, sensitivity, synchronization, and offline behavior.

CSSHTMLJavaScript

Architecture scenarioMedium~10 min

How would you structure JavaScript module boundaries so code remains reusable and unused code can be removed safely?

Designs explicit ESM boundaries with focused exports, controlled side effects, and dependency direction that supports safe bundling.

Debugging scenarioHard~15 min

Some users receive an old HTML shell with new assets, or a new shell that requests deleted chunks after deployment. How would you diagnose and prevent it?

Diagnoses incompatible cached HTML and immutable assets across CDN, browser, service-worker, and rollout boundaries.

CSSHTMLJavaScript

Debugging scenarioMedium~10 min

Two parts of a UI unexpectedly change the same object. How would you explain and fix the shared-reference mutation?

Diagnoses aliasing and shallow-copy mistakes, then restores explicit state ownership and immutable update boundaries.

Concept questionEasy~5 min

What does structural typing mean in TypeScript, and where can it surprise you?

Explains assignability by shape, excess-property checks, and the gap between compile-time compatibility and runtime identity.

JavaScriptTypeScript

Concept questionEasy~5 min

What is a closure in JavaScript, and when is it useful or surprising?

Explains closures as functions retaining access to lexical bindings, then connects them to callbacks, factories, state, and common capture mistakes.

Architecture scenarioMedium~10 min

When do utility and mapped types improve a TypeScript model, and when do they hide the domain contract?

Uses derived types for genuine relationships while preserving explicit boundaries for domain and transport models.

JavaScriptTypeScript

Comparison questionMedium~7 min

When should you use a type annotation, a type assertion, or satisfies?

Separates declared variable types, unchecked developer assertions, and compatibility checking that preserves useful inferred types.

JavaScriptTypeScript

Comparison questionMedium~7 min

When would you use Promise.all, allSettled, race, or any?

Chooses promise combinators by success criteria, failure semantics, cancellation needs, and the fate of losing operations.

Comparison questionEasy~5 min

Which JavaScript equality and coercion rules matter in application code, and how do you avoid surprising comparisons?

Prioritizes explicit normalization, strict equality, object identity, nullish handling, and NaN over coercion puzzles.