Technical interview questions and drills

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Showing the Frontend Engineering Foundations curriculum. Technology tags describe each drill's actual implementation context; shared drills can belong to more than one track.

Debugging scenarioMedium~10 min

A CSS rule appears correct but does not win, or unexpectedly affects descendants. How would you debug the cascade?

Debugs matched rules, cascade origin, importance, layers, specificity, source order, inheritance, and computed values.

In Frontend Engineering Foundations

CSSHTML

Debugging scenarioMedium

Drills

A CSS rule appears correct but does not win, or unexpectedly affects descendants. How would you debug the cascade?

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

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

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

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?

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

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

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

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

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

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

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

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?

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

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

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

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

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

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

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