Intermediate interview questions in Frontend Dev, page 3
Use useContext to provide theme state without prop drilling
This tests global state sharing without prop drilling. A strong answer uses createContext and a Provider with useState at the app root, then calls useContext in nested components. Red flag: ignoring re-render costs or placing the Provider too deep.
Explicit vs implicit grid: how do you control implicit tracks?
Explicit tracks use grid-template; implicit tracks appear on overflow. Control via grid-auto-rows/columns and grid-auto-flow.
Compile-time vs runtime prop validation across frameworks?
TypeScript (compile-time) catches errors before build; Vue props validation (runtime) catches at runtime; tradeoff: TS is stricter, Vue validation is flexible but less safe.
How do you type a GeoJSON Coordinate tuple and LineString array?
Tests fixed-length tuple typing versus flexible arrays in TypeScript. A strong answer uses [number, number] for Coordinate, then Coordinate[] for LineString, and explains why number[] loses length safety. Red flag: using number[] or objects instead of tuples.
Explain the difference between useMemo and useCallback
This tests whether useMemo caches values while useCallback caches functions, and why that matters for React.memo. A strong answer notes React.memo uses Object.is, so a new inline function prop triggers a child re-render. Red flag: claiming they are the same.
Implement a fixed-width sidebar with Flexbox and CSS Grid
This tests Flexbox as one-dimensional versus Grid as 2-dimensional. A strong answer covers Flexbox with flex: 1 on main and flex: none on sidebar, and Grid with grid-template-columns: 250px 1fr. Red flag: claiming Grid is always superior or ignoring overflow.
Compare multiple boolean props versus a single status string prop
Booleans let callers pass conflicting flags like isLoading plus isError, leaking implementation priority; a single status enum makes invalid states unrepresentable.
Compare HOCs and custom hooks for sharing logic
Tests your grasp of React's shift from wrapper-based to function-based logic reuse. Hooks eliminate wrapper hell and implicit props by extracting stateful behavior into plain functions without nesting components. Red flag: calling hooks just sugar.
How do you type a function with string and number overloads?
Tests if you know overloads are public API and the implementation uses a union. Answer: write process(string):string and process(number):number overloads, then implement with string|number and narrow. Red flag: exposing only the implementation signature.
Why does this lose context in class callbacks and two TypeScript fixes?
This tests runtime this binding. Explain that regular functions get this from the call site, so passing a method strips its object context. Fix with an arrow property or constructor bind. Red flag: var self = this or claiming TypeScript changes binding.
Explain key or trackBy in list rendering and index key risks
Your understanding of virtual DOM reconciliation and stable element identity. A good answer covers that key binds DOM state to data identity, and that index keys break reordering by recycling wrong components.
What is the purpose of the implements keyword?
Tests compile-time contract enforcement in TypeScript. Explain that implements checks class-to-interface compatibility at compile time with no runtime overhead, then code a CacheService with get and set methods.
How would you create a styled Button accepting a variant prop
It tests prop interpolation for dynamic styling in CSS-in-JS. Good answers use styled.button with a function reading props.variant to map CSS rules in one component. A red flag is splitting into separate components per variant or using inline styles.
Key differences between responsive and adaptive design, and when to choose adaptive
It tests layout strategy trade-offs beyond media queries. A strong answer contrasts responsive fluid grids with adaptive device-specific layouts. Red flag: claiming they are identical or that adaptive means more breakpoints.
How do you pass markup from a parent to a child component?
This tests declarative composition for UI reuse. A strong answer covers default and named slot syntax in Vue/Svelte (slot outlet, v-slot) or Angular ng-content with select for named projection.
Implement a light/dark theming system with CSS-in-JS and React Context
This tests React Context architecture with CSS-in-JS theme injection. Strong answers include: a Theme Context with mode and toggle; ThemeProvider at the app root; consumption via useTheme or props.theme.
Build a responsive 3-column layout with Flexbox and Grid
Tests whether you pick right tool for responsive layouts. Good answers use flex-wrap and flex-basis for Flexbox, repeat() or grid-template-areas for Grid, in min-width 768px query. Red flag: desktop-first max-width queries or claiming Grid replaces Flexbox.
Why does todos.push miss Svelte updates but spread works?
Tests compile-time versus runtime reactivity. Answer: Svelte's compiler instruments assignments, not method calls, so push is invisible; Vue Proxies and Angular Zone.js both intercept push to trigger updates.
How would you use srcset and sizes for responsive image performance?
This tests responsive image selection in the browser. A strong answer covers srcset with w or x descriptors, sizes for layout width hints, and the browser picking before CSS loads. Red flag: suggesting JS detection or CSS backgrounds instead.
What's the difference between Angular property and attribute binding?
Tests whether you know Angular binds to DOM properties by default. [disabled] sets a DOM property; [attr.role] sets an HTML attribute. Use attribute binding when no DOM property exists, such as SVG attributes or role. Red flag: claiming they are equivalent.
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