JavaScript

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.

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.

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.

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.

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.

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.

Frontend Engineering Foundations

Shared JavaScript, TypeScript, browser, and CSS foundations for modern frontend interviews.

A framework-neutral frontend foundation covering JavaScript semantics, TypeScript contracts, browser rendering, CSS diagnosis, storage, caching, and production deployment failures.