Frontend Development Interview Questions for 1 Year Experience
40 questions with answers for candidates with 1 year of experience — 15 easy, 25 medium.
What interviewers expect: 1 year experience
With one year of experience, expect deeper JavaScript and TypeScript questions, API integration with error and loading states, browser storage, accessibility basics and Git workflows. Interviewers ask about features you shipped, bugs you fixed and how you tested them. A machine coding round building a small app in 60 to 90 minutes is common.
This set is weighted towards CSS Architecture and Accessibility (7), Browser APIs (6), Modern JavaScript (6), TypeScript (6).
Machine coding TypeScript usage API handling Testing basics
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Code splitting breaks a large JavaScript bundle into smaller chunks so the browser downloads only what the current page needs. Lazy loading defers loading code or assets until they are required, using dynamic import() for components like a chart or a rich text editor. Route-based splitting is the most common starting point. It reduces initial download and parse time, which improves LCP and INP on slower devices.
02
Implement a copy-to-clipboard button with user feedback.
The async Clipboard API works in secure contexts after a user action:
copyBtn.addEventListener('click', async () => {
try {
await navigator.clipboard.writeText(couponCode.textContent);
copyBtn.textContent = 'Copied!';
} catch {
copyBtn.textContent = 'Press Ctrl+C to copy';
}
setTimeout(() => (copyBtn.textContent = 'Copy code'), 2000);
});
An aria-live region can announce 'Copied' to screen reader users, since a changing button label may not always be read out.
Tokens go in CSS with the @theme directive:
@import 'tailwindcss';
@theme {
--color-brand-500: #2563eb;
--color-brand-700: #1d4ed8;
--font-display: 'Poppins', sans-serif;
--radius-card: 12px;
}
/* usage in markup */
/* <button class='bg-brand-500 hover:bg-brand-700 rounded-card font-display'> */
Tailwind generates utilities like bg-brand-500 from these variables and also exposes them as CSS custom properties for use in plain CSS.
04
Compare Promise.all, Promise.allSettled, Promise.race and Promise.any.
Promise.all resolves with all results when every promise succeeds, but rejects immediately if any fails. Promise.allSettled always waits for all and returns each outcome with status fulfilled or rejected, useful for dashboards loading independent widgets. Promise.race settles with the first promise to settle, often used for timeouts. Promise.any resolves with the first success and rejects only if all fail, useful for trying multiple mirrors.
05
A third-party library you need has no TypeScript types. What do you do?
First I check if types exist on DefinitelyTyped by installing @types/library-name. If not, I write a minimal declaration file, for example declare module 'old-chart-lib' with only the functions I use, in a types folder included by tsconfig. This is better than a blanket any import. If the library is important to the community, contributing those types upstream helps everyone.
Snapshot tests save a component's rendered output and fail when it changes, which quickly detects unintended changes with little effort. However, large snapshots are hard to review, so developers often update them blindly, and they break on harmless markup changes. They work best for small, stable outputs like serialised config or error messages. For UI behaviour, explicit assertions on visible text and roles are more meaningful.
07
Animate a modal smoothly when it opens without causing layout work.
Animate only transform and opacity, which run on the compositor:
.modal {
opacity: 0;
transform: translateY(16px) scale(0.98);
transition: opacity 200ms ease, transform 200ms ease;
}
.modal.is-open {
opacity: 1;
transform: none;
}
@media (prefers-reduced-motion: reduce) {
.modal { transition: opacity 100ms linear; transform: none; }
}
Animating top, height or margin instead would trigger layout on every frame and cause jank on low-end phones.
08
What is a JavaScript bundler and why do frontend projects need one?
A bundler takes your source files, follows imports to build a dependency graph and outputs optimised files for the browser. Along the way it transpiles TypeScript and JSX, processes CSS, handles images, minifies code, removes unused exports and adds content hashes for caching. Native ES modules work in browsers, but loading hundreds of unoptimised files is slow, so production builds still use bundlers like Vite, webpack or Rspack.
09
When should you use Map and Set instead of plain objects and arrays?
Map allows keys of any type, keeps insertion order, has a size property and performs well with frequent additions and deletions, so it suits caches and lookups by object. Set stores unique values with fast has() checks, ideal for tracking selected ids. Plain objects are better for fixed-shape records and JSON. Arrays are better when order and index access matter and duplicates are allowed.
10
Explain the utility types Partial, Pick, Omit and Record.
Partial<T> makes all properties optional, useful for update payloads. Pick<T, 'id' | 'name'> creates a type with only selected keys, and Omit<T, 'password'> removes keys, handy for public user objects. Record<K, V> builds an object type with keys K and values V, such as Record<'en' | 'hi', string> for translations. Others include Required, Readonly, ReturnType and Awaited.
11
How can you communicate between multiple tabs of the same site?
BroadcastChannel lets same-origin tabs, windows and workers publish and subscribe to messages on a named channel, which suits syncing logout, theme or cart updates. The storage event fires in other tabs when localStorage changes, which is a simple fallback. SharedWorker can hold shared state for all tabs. Each option works only within the same origin, so cross-domain sync needs a server or postMessage.
12
What are the URL and URLSearchParams APIs used for?
The URL constructor parses a URL into parts like hostname, pathname and searchParams, and builds valid URLs without manual string concatenation. URLSearchParams reads and writes query strings, handling encoding automatically, for example params.get('page') or params.set('sort', 'price'). They prevent bugs with special characters such as spaces and ampersands in search terms, and are the clean way to sync filters with the address bar.
13
What is Interaction to Next Paint and what usually makes it poor?
INP replaced First Input Delay in 2024. It measures the delay from a click, tap or key press until the next frame is painted, across all interactions on the page, reporting roughly the worst one. Poor INP usually comes from long JavaScript tasks blocking the main thread, heavy event handlers, large re-renders and expensive layout work after interaction. Breaking up tasks and showing immediate visual feedback improves it.
preconnect opens an early connection, including DNS, TCP and TLS, to an important third-party origin like a font or API server. preload fetches a resource needed for the current page at high priority, such as the hero image or main font. prefetch downloads resources likely needed for the next navigation at low priority during idle time. Overusing preload wastes bandwidth and can delay more critical resources.
15
Search results sometimes show data for an older query. What is happening?
This is a race condition: requests for 'ja' and 'java' are in flight together, and if the older one responds last, it overwrites the newer results. I would cancel the previous request with AbortController, or tag each request with an id and ignore responses that are not the latest. Debouncing the input reduces the number of requests, and caching repeated queries makes responses faster and more consistent.
16
npm audit reports a critical vulnerability in a dependency. What do you do?
I would check whether the vulnerable package is actually used in the production bundle or only in build tooling, and whether the vulnerable code path is reachable. Then I would update to a patched version, using npm update or overrides for transitive dependencies. If no fix exists, I would look for an alternative package or mitigate. Automated tools like Dependabot or Renovate keep dependencies current.
17
How does Tailwind CSS keep the final CSS file small?
Tailwind scans your source files for class names and generates only the utilities you actually use, so the production CSS is usually a few kilobytes even though thousands of utilities are available. This requires class names to appear as complete strings in the code. Tailwind v4 uses a CSS-first configuration with @theme for design tokens and detects source files automatically.
18
How do you handle a designer who expects pixel-perfect matching on every device?
Situation: a designer flagged small spacing differences between Figma and my build on several phones. Task: I needed to address concerns while keeping the layout fluid. Action: I fixed genuine mistakes immediately, then showed how fixed pixel values would break on other screens and proposed shared spacing tokens. Result: we agreed on tokens and breakpoints, and future handoffs had far fewer revision rounds.
19
What is the guiding principle of Testing Library and why query by role?
Testing Library encourages testing the way users interact: find elements by what they see and hear, not by implementation details like class names or component internals. getByRole('button', { name: 'Submit' }) is preferred because it also verifies the element is accessible. Tests written this way survive refactors and catch real accessibility problems. Test ids are a last resort when no accessible query works.
A tagged template is a function placed before a template literal, like html`<p>${name}</p>`. The function receives the static string parts as an array and the interpolated values separately, so it can escape, transform or validate values before joining them. Libraries use this pattern for safe HTML templating, CSS-in-JS and GraphQL queries. Normal template literals simply interpolate values and support multi-line strings.
A union type A | B means the value can be either type, such as string | number or 'success' | 'error'. You must narrow it before using type-specific members. An intersection type A & B combines all properties of both, for example User & { permissions: string[] } adds a field to an existing type. Unions model alternatives, while intersections model composition of features.
22
How do you handle unclear requirements from a product manager?
Situation: a product manager asked for 'offline support' in our web app without details. Task: I needed clarity before estimating. Action: I listed specific questions, which screens, read-only or editing, how long offline, and shared a quick prototype showing two options with effort estimates. Result: we agreed on read-only offline access for the order history, which shipped in one sprint instead of an open-ended project.
23
Create a type where all fields are optional except id.
Real time makes tests slow and nondeterministic. I would use fake timers, such as vi.useFakeTimers() and vi.setSystemTime(new Date('2026-11-12T10:00:00+05:30')), then advance time with vi.advanceTimersByTime to test debounce, countdowns or expiry logic instantly. Restoring real timers after each test avoids leaking state. Designing functions to accept a clock or date parameter makes them even easier to test.
Component-driven development builds UIs from the bottom up as small, reusable, isolated components, such as buttons and inputs, composed into larger patterns like forms and pages. Each component has a clear API through props or attributes and is developed and documented in isolation, often in Storybook. Composition over configuration keeps components flexible. This approach enables design systems, parallel work and easier testing.
26
What are pure functions and why does immutability matter in frontend code?
A pure function returns the same output for the same input and has no side effects such as changing external variables. Immutability means creating new objects instead of modifying existing ones, for example using spread syntax to update state. Together they make code predictable and easy to test, and they let frameworks detect changes with a simple reference comparison, which enables efficient re-rendering.
27
Model API request state with a discriminated union.
A shared status field lets TypeScript narrow each case:
type ApiState<T> =
| { status: 'idle' }
| { status: 'loading' }
| { status: 'success'; data: T }
| { status: 'error'; message: string };
function render(state: ApiState<string[]>) {
switch (state.status) {
case 'success': return state.data.join(', ');
case 'error': return 'Error: ' + state.message;
default: return 'Loading...';
}
}
Impossible states, like having both data and an error, cannot be represented.
28
Tell me about a time you received critical feedback in a code review.
Situation: a senior engineer rejected my pull request for a new dashboard because the CSS was hard to maintain. Task: I had to rework it without missing the sprint. Action: I asked for a short call to understand the concerns, refactored styles into reusable components with tokens, and added notes explaining my choices. Result: the PR was approved, and the components were later reused in two other screens.
Use a dynamic import inside the event handler:
const exportBtn = document.querySelector('#export-pdf');
exportBtn.addEventListener('click', async () => {
exportBtn.disabled = true;
const { generatePdf } = await import('./pdf-export.js');
await generatePdf(reportData);
exportBtn.disabled = false;
});
The bundler creates a separate chunk for pdf-export.js, so users who never export do not download it. Prefetching on hover can hide the delay.
30
Tailwind classes built dynamically like 'bg-' + colour work locally but are missing in production. Why?
Tailwind finds classes by scanning source files for complete strings, so a class assembled at runtime never appears in the code and its CSS is not generated. The fix is to map values to full class names, such as const colours = { success: 'bg-green-600', error: 'bg-red-600' }. If truly dynamic values are needed, use inline styles with CSS variables or explicitly safelist those classes.
31
In a single-page app, the back button takes users out of the site instead of to the previous filter. Why?
The app changes the view without adding history entries, so the browser has nothing to go back to within the site. Each meaningful navigation, like changing a category or opening a product, should call pushState or the router's navigate function, while minor changes such as typing in search can use replaceState. The app must also listen to popstate and restore the view and scroll position from the URL.
32
What are source maps and should they be deployed to production?
Source maps link minified production code back to the original source files and line numbers, so DevTools and error trackers show readable stack traces. They are generated by the bundler as .map files. Many teams upload them privately to monitoring tools like Sentry and do not serve them publicly, which keeps original source code less exposed while still allowing debugging of production errors.
33
Why are dvh and svh units better than vh on mobile?
On mobile browsers, 100vh equals the height with the address bar hidden, so a full-screen section gets cut off when the bar is visible. svh is the small viewport height with browser UI shown, lvh the large one, and dvh updates dynamically as the bar appears or hides. Using min-height: 100dvh for hero sections or app shells prevents content hiding behind browser chrome.
34
Write a Playwright end-to-end test for a login flow.
Use role-based locators and web-first assertions:
import { test, expect } from '@playwright/test';
test('user can log in and see dashboard', async ({ page }) => {
await page.goto('/login');
await page.getByLabel('Email').fill('student@example.com');
await page.getByLabel('Password').fill('Secret@123');
await page.getByRole('button', { name: 'Log in' }).click();
await expect(page).toHaveURL(/dashboard/);
await expect(page.getByRole('heading', { name: 'My courses' })).toBeVisible();
});
Assertions auto-wait, so no manual sleeps are needed. Save login state with storageState to reuse in other tests.
35
Product images on a listing page load slowly. What quick fixes would you apply?
I would convert images to WebP or AVIF, resize them to the actual thumbnail size instead of loading full product photos, and serve them through srcset. Images below the fold get loading='lazy', while the first few visible ones load eagerly. Adding width and height prevents layout shift, and serving images from a CDN with long cache headers makes repeat visits much faster.
36
What is the testing pyramid, and how does the testing trophy differ?
The testing pyramid suggests many fast unit tests, fewer integration tests and very few slow end-to-end tests. The testing trophy, popular for frontend work, puts most effort into integration tests that render components with real behaviour, supported by static analysis like TypeScript and ESLint at the base. Both aim for confidence at reasonable cost; the trophy reflects that UI bugs often appear where units connect.
37
Set up ESLint with the flat config for a TypeScript project.
Install packages and create eslint.config.js:
// npm i -D eslint @eslint/js typescript-eslint
import js from '@eslint/js';
import tseslint from 'typescript-eslint';
export default tseslint.config(
js.configs.recommended,
...tseslint.configs.recommended,
{
rules: {
'@typescript-eslint/no-explicit-any': 'warn',
'no-console': ['warn', { allow: ['error'] }]
}
},
{ ignores: ['dist/'] }
);
Run npx eslint . locally and in CI. Leave formatting to Prettier so the two tools do not conflict.
38
Editing one item in a copied list also changes the original list. Why?
Copying an array with spread or slice creates a new array, but the objects inside are still the same references. Changing copy[0].qty changes the original object too. The fix is to create new objects for changed items, for example list.map(item => item.id === id ? { ...item, qty: item.qty + 1 } : item), or use structuredClone when a full deep copy is genuinely needed.
39
Write a type-safe getProperty function using generics and keyof.
Constrain the key to the object's own keys:
function getProperty<T, K extends keyof T>(obj: T, key: K): T[K] {
return obj[key];
}
const course = { title: 'Frontend', weeks: 14 };
const weeks = getProperty(course, 'weeks'); // number
// getProperty(course, 'price'); // compile error
T[K] is an indexed access type, so the return type matches the chosen property. Typos in key names are caught at compile time.
40
Compare IntersectionObserver, ResizeObserver and MutationObserver.
IntersectionObserver reports when an element enters or leaves the viewport or a container, used for lazy loading, infinite scroll and analytics impressions. ResizeObserver reports changes to an element's size, useful for charts that must redraw when their container changes. MutationObserver reports DOM changes like added nodes or changed attributes. All three are asynchronous and far more efficient than polling or scroll and resize listeners.
Frequently asked questions
What is asked in Frontend Development interviews for 1 year of experience?
With one year of experience, expect deeper JavaScript and TypeScript questions, API integration with error and loading states, browser storage, accessibility basics and Git workflows. Interviewers ask about features you shipped, bugs you fixed and how you tested them. A machine coding round building a small app in 60 to 90 minutes is common.
How many questions should I practise before a Frontend Development interview?
Work through all 40 questions here, then the company-wise sets for the employers you are targeting. Quality matters more than count: be able to explain why each answer is right.
Which topics matter most for 1 year of experience?
Focus first on Machine coding, TypeScript usage, API handling, Testing basics.