MEAN Stack Interview Questions in Kolkata

Group validators see all child controls. export const passwordsMatch: ValidatorFn = (group: AbstractControl) => { const pass = group.get('password')?.value; const confirm = group.get('confirm')?.value; return pass && confirm && pass !== confirm ? { passwordMismatch: true } : null; }; form = this.fb.group( { password: ['', Validators.required], confirm: ['', Validators.required] }, { validators: passwordsMatch } ); // @if (form.hasError('passwordMismatch') && form.controls.confirm.touched) { ... }

A typical strict configuration: { "compilerOptions": { "target": "ES2022", "module": "NodeNext", "moduleResolution": "NodeNext", "outDir": "dist", "rootDir": "src", "strict": true, "noUncheckedIndexedAccess": true, "esModuleInterop": true, "skipLibCheck": true, "sourceMap": true }, "include": ["src"] } noUncheckedIndexedAccess adds undefined to indexed lookups, catching missing keys.

A ValidatorFn returns null or an error map. import { AbstractControl, ValidationErrors, ValidatorFn } from '@angular/forms'; export function strongPassword(): ValidatorFn { return (control: AbstractControl): ValidationErrors | null => { const value = control.value as string; if (!value) return null; const ok = /[A-Z]/.test(value) && /\d/.test(value); return ok ? null : { weakPassword: true }; }; } // password: ['', [Validators.required, strongPassword()]] // @if (form.controls.password.hasError('weakPassword')) { ... }

Reusable middleware with typed output. import { z, ZodSchema } from 'zod'; import { RequestHandler } from 'express'; export const validateBody = (schema: ZodSchema): RequestHandler => (req, res, next) => { const parsed = schema.safeParse(req.body); if (!parsed.success) { return res.status(400).json({ errors: parsed.error.flatten().fieldErrors }); } req.body = parsed.data; next(); }; const createOrder = z.object({ items: z.array(z.object({ productId: z.string(), qty: z.number().int().min(1) })).min(1), address: z.string().min(10) }); router.post('/orders', validateBody(createOrder), ordersController.create);

Tokens carry non-class values. import { InjectionToken, inject, Injectable } from '@angular/core'; export interface AppConfig { apiUrl: string; pageSize: number } export const APP_CONFIG = new InjectionToken<AppConfig>('APP_CONFIG'); // app.config.ts providers: [{ provide: APP_CONFIG, useValue: { apiUrl: environment.apiUrl, pageSize: 20 } }] @Injectable({ providedIn: 'root' }) export class OrderService { private config = inject(APP_CONFIG); private http = inject(HttpClient); list() { return this.http.get(`${this.config.apiUrl}/orders`, { params: { limit: this.config.pageSize } }); } }

Register with provideHttpClient(withInterceptors([authInterceptor])). export const authInterceptor: HttpInterceptorFn = (req, next) => { const auth = inject(AuthService); const router = inject(Router); const token = auth.token(); const authReq = token ? req.clone({ setHeaders: { Authorization: `Bearer ${token}` } }) : req; return next(authReq).pipe( catchError((err: HttpErrorResponse) => { if (err.status === 401) { auth.logout(); router.navigate(['/login']); } return throwError(() => err); }) ); };

Signals and built-in control flow keep it concise. import { Component, signal } from '@angular/core'; import { CurrencyPipe } from '@angular/common'; @Component({ selector: 'app-product-list', imports: [CurrencyPipe], template: ` @for (p of products(); track p.id) { <div class='card'>{{ p.name }} - {{ p.price | currency:'INR' }}</div> } @empty { <p>No products found</p> } ` }) export class ProductListComponent { products = signal([{ id: 1, name: 'Laptop', price: 55000 }]); }

Expose read-only state and mutation methods. @Injectable({ providedIn: 'root' }) export class CartService { private items = signal<CartItem[]>([]); readonly cart = this.items.asReadonly(); readonly count = computed(() => this.items().reduce((n, i) => n + i.qty, 0)); readonly total = computed(() => this.items().reduce((s, i) => s + i.qty * i.price, 0)); add(product: Product) { this.items.update((list) => { const found = list.find((i) => i.id === product.id); return found ? list.map((i) => (i.id === product.id ? { ...i, qty: i.qty + 1 } : i)) : [...list, { ...product, qty: 1 }]; }); } remove(id: string) { this.items.update((l) => l.filter((i) => i.id !== id)); } }

Useful diagnostic commands: db.orders.getIndexes() db.orders.find({ status: 'pending', city: 'Pune' }) .sort({ createdAt: -1 }) .explain('executionStats') db.setProfilingLevel(1, { slowms: 100 }) db.system.profile.find().sort({ ts: -1 }).limit(5) db.orders.createIndex({ status: 1, city: 1, createdAt: -1 }) Compare totalDocsExamined with nReturned before and after creating the index.

proxy.conf.json in the Angular project: { "/api": { "target": "http://localhost:3000", "secure": false, "changeOrigin": true, "logLevel": "debug" } } angular.json, under serve options: "proxyConfig": "proxy.conf.json" Then call relative URLs in services, such as this.http.get('/api/products'), and run ng serve. The browser talks only to the dev server, so no CORS setup is needed locally.

One domain, no CORS needed. server { listen 80; server_name shop.example.com; root /usr/share/nginx/html; location /api/ { proxy_pass http://api:3000; proxy_set_header Host $host; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } location / { try_files $uri $uri/ /index.html; } location ~* \.(js|css|woff2)$ { expires 1y; add_header Cache-Control "public, immutable"; } } Angular hashed file names make long caching safe.

Return a UrlTree to redirect. import { inject } from '@angular/core'; import { CanActivateFn, Router } from '@angular/router'; import { AuthService } from './auth.service'; export const authGuard: CanActivateFn = (route, state) => { const auth = inject(AuthService); const router = inject(Router); return auth.isLoggedIn() ? true : router.createUrlTree(['/login'], { queryParams: { returnUrl: state.url } }); }; // { path: 'orders', canActivate: [authGuard], loadComponent: ... }