Intermediate interview questions in Frontend Dev, page 5
Explain the inverted triangle of ITCSS
ITCSS orders layers from far-reaching low-specificity (settings, tools, generic) down to localized high-specificity (components, utilities), so specificity climbs gradually.
How do you use a Server Action for form submission and useFormState?
Tests server-client form state orchestration. Outline: write a Server Action that validates and returns errors; pass it to useFormState for state; wire to form action and use useFormStatus for pending UI.
Compare Angular's three ViewEncapsulation modes and give a use case.
This tests style isolation tradeoffs. Emulated scopes CSS with unique attributes, ShadowDom uses native shadow roots, and None disables scoping. Switch to ShadowDom for strict boundaries or None for global themes.
What deep selector pierces Vue scoped styles, and why use it cautiously?
This tests Vue scoped CSS encapsulation. Use :deep() to target child internals from a scoped block, but it breaks encapsulation and creates brittle coupling. A red flag is recommending deprecated /deep/ or unscoped global styles.
How do CSS Modules differ from Vue scoped CSS?
This question tests build-time versus compiler style isolation. CSS Modules export a hashed class mapping object; Vue scoped CSS adds unique data-attributes. You bind templates via $style.myClass or an imported object. Red flag: claiming both use attributes.
How do _ngcontent and _nghost attributes enforce Angular style isolation?
Unique component ID, _nghost on host, _ngcontent on template nodes, and CSS rewritten with attribute selectors to scope styles.
Write a typed async fetchUser with error handling
Tests promise-based fetch plus TypeScript return-type contracts. A strong answer checks response.ok before response.json() and types the return as Promise<User>. A red flag is swallowing 4xx/5xx errors silently.
How do you include a JWT in a fetch request?
Tests knowledge of the fetch options object and Bearer scheme syntax. A strong answer sets headers: { Authorization: Bearer <token> } as the second argument and notes fetch does not auto-attach tokens. Red flag: omitting Bearer or hardcoding secrets.
How do you handle an API returning 200 for success and failure?
This tests TypeScript narrowing and runtime validation of ambiguous 200 responses. A strong answer uses a discriminated union, narrows with a type guard, and validates shape before branching. Red flag: casting the body with as and skipping runtime checks.
When can overusing useMemo hurt performance and what are the trade-offs?
Memoizing cheap work wastes cycles, increases memory use, and burdens dependency tracking.
Sass @mixin versus @extend
@mixin copies declarations into each caller, accepts arguments, and can duplicate code; @extend groups selectors sharing one rule via a comma list, reducing duplication but coupling selectors.
Create a generic fetchJson wrapper with typed response and error handling
Generic T parameter, optional RequestInit, throw if !res.ok, return res.json() as Promise<T>.
How do React.lazy and dynamic import() enable code splitting?
It tests your grasp of React code-splitting and the Suspense contract. A strong answer states that lazy defers loading until first render via dynamic import, and Suspense shows a fallback while the Promise resolves.
What is PostCSS and how it differs from Sass
PostCSS is a plugin-driven tool that parses CSS into an AST and transforms it; it is not a fixed language like Sass but a platform for plugins like autoprefixer.
How does Next.js routing auto-implement code splitting?
Tests route-based code splitting versus manual setup. Strong answers note each page/route becomes its own chunk automatically, while client-only apps need explicit React.lazy and Suspense.
Build a DRY button with Sass maps and mixins
A base mixin for shared button styles, a variants map of name to colors looped to generate modifiers, and a sizes map looped for sizing.
React Profiler long render duration: causes and next steps?
Tests interpreting actualDuration vs baseDuration. Outline: close values on updates mean broken memoization—add memo or useMemo; high baseDuration alone means an inherently slow subtree. Red flag: proposing fixes before comparing these two Profiler metrics.
What does autoprefixer do and why?
Autoprefixer is a PostCSS plugin that adds vendor prefixes to CSS based on a browserslist target using compatibility data, so you write standard CSS and it handles support.
Validate matching Vue passwords: computed property or watcher?
Use a computed boolean for caching and dependency tracking; reserve watchers for side effects only.
How do you debounce input for API validation in Vue or Angular?
Tests reactive stream control and cancellation. A strong answer uses debounceTime at 300ms, switches with switchMap, and handles loading and error states. Red flag: using setTimeout without cleanup or ignoring race conditions.
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