Frontend Development Interview Questions in Visakhapatnam

This hides content visually but keeps it readable by assistive technology: .sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; } Use it for labels on icon-only buttons, such as <button><svg aria-hidden='true'></svg><span class='sr-only'>Close</span></button>. display: none would hide the text from screen readers too.

Use AbortController inside useEffect: import { useEffect, useState } from 'react'; export function useFetch(url) { const [state, setState] = useState({ data: null, error: null, loading: true }); useEffect(() => { const controller = new AbortController(); setState(s => ({ ...s, loading: true })); fetch(url, { signal: controller.signal }) .then(r => (r.ok ? r.json() : Promise.reject(new Error(r.status)))) .then(data => setState({ data, error: null, loading: false })) .catch(err => { if (err.name !== 'AbortError') setState({ data: null, error: err, loading: false }); }); return () => controller.abort(); }, [url]); return state; } In production apps, TanStack Query adds caching and retries.

Test normal, edge and invalid inputs: // format.ts export const formatINR = (paise: number) => new Intl.NumberFormat('en-IN', { style: 'currency', currency: 'INR' }).format(paise / 100); // format.test.ts import { describe, it, expect } from 'vitest'; import { formatINR } from './format'; describe('formatINR', () => { it('formats lakhs with Indian grouping', () => { expect(formatINR(12345600)).toBe('\u20b91,23,456.00'); }); it('handles zero', () => { expect(formatINR(0)).toBe('\u20b90.00'); }); });

Read params on load and update them without reload: const params = new URLSearchParams(location.search); const category = params.get('category') ?? 'all'; applyFilters({ category }); function updateFilter(key, value) { const p = new URLSearchParams(location.search); value ? p.set(key, value) : p.delete(key); history.pushState(null, '', '?' + p.toString()); applyFilters(Object.fromEntries(p)); } window.addEventListener('popstate', () => applyFilters(Object.fromEntries(new URLSearchParams(location.search)))); Users can now share and bookmark filtered views.

Stub the global fetch and assert behaviour: import { it, expect, vi, afterEach } from 'vitest'; import { loadCourses } from './api'; afterEach(() => vi.unstubAllGlobals()); it('returns an empty list when the server fails', async () => { vi.stubGlobal('fetch', vi.fn().mockResolvedValue( new Response('Server error', { status: 500 }) )); const result = await loadCourses(); expect(result).toEqual([]); expect(fetch).toHaveBeenCalledWith('/api/courses'); }); For larger suites, MSW handlers are cleaner than stubbing fetch in every test.

Load flags once and check them where needed: let flags = {}; export async function loadFlags(userId) { const res = await fetch('/api/flags?user=' + encodeURIComponent(userId)); flags = res.ok ? await res.json() : {}; } export const isEnabled = (name) => flags[name] === true; // usage await loadFlags(currentUser.id); if (isEnabled('new-checkout')) renderNewCheckout(); else renderOldCheckout(); Defaulting to off when the request fails keeps the stable path. Flags enable gradual rollouts, but old flags must be removed to avoid clutter.

A store holds state and notifies subscribers: function createStore(initial) { let state = initial; const listeners = new Set(); return { get: () => state, set(update) { state = { ...state, ...update }; listeners.forEach(fn => fn(state)); }, subscribe(fn) { listeners.add(fn); return () => listeners.delete(fn); } }; } const cart = createStore({ items: 0 }); const stop = cart.subscribe(s => (badge.textContent = s.items)); cart.set({ items: 2 }); The returned unsubscribe function prevents memory leaks.

Let callers specify the expected response type: async function getJson<T>(url: string): Promise<T> { const res = await fetch(url); if (!res.ok) throw new Error(`Request failed: ${res.status}`); return res.json() as Promise<T>; } interface Course { id: number; title: string; } const courses = await getJson<Course[]>('/api/courses'); courses[0].title.toUpperCase(); The cast trusts the server, so for untrusted data validate with a schema library like Zod before returning.

Retry on network errors and 5xx responses, doubling the delay each time: async function fetchWithRetry(url, options = {}, retries = 3, delay = 500) { try { const res = await fetch(url, options); if (res.status >= 500 && retries > 0) throw new Error('Server ' + res.status); return res; } catch (err) { if (retries === 0) throw err; await new Promise(r => setTimeout(r, delay)); return fetchWithRetry(url, options, retries - 1, delay * 2); } } Do not retry 4xx errors, and only retry idempotent requests.

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.