MERN Stack Developer: Free Skill Evaluation

How the Internet Works Client/Server Architecture HTTP Fundamentals Status Codes Document structure Semantic HTML Headings Forms Inputs Buttons Tables Media Links Accessibility fundamentals Metadata Selectors Box model Typography Positioning Flexbox CSS Grid Variables Transitions Animations Desktop Tablet Android IPhone Breakpoints Mobile-first design Responsive images Fluid layout Touch targets Let Const Primitive types Objects Operators Conditions Loops Functions Arrays Maps Sets Strings Map Filter Reduce Find Some Every Sort Declarations Expressions Arrow functions Callbacks Higher-order functions Lexical scope Execution context Call stack Scope Lexical environment Hoisting Closures This Prototype Prototype chain Destructuring Spread Rest Template literals Optional chaining Nullish coalescing ES modules Dynamic imports Callback Promise Async Await Promise.all Promise.allSettled Error handling Task queue Microtask queue Promise callbacks Timers Node/browser differences conceptually DOM Events LocalStorage SessionStorage Fetch API URL APIs Repository Commits Branches Merges Conflicts Pull requests Reviews Tags Type annotations Primitives Tuples Enums awareness Interfaces Type aliases Unions Intersections Generics Utility types Narrowing Discriminated unions Keyof Mapped types concepts Typescript For Apis React architecture JSX Components Props State Conditional rendering Lists Keys UseState UseEffect UseRef UseMemo UseCallback UseContext Custom hooks Presentational Components Container concepts Composition Reusable Components Controlled Components Routes Dynamic routes Nested routes Protected routes Layouts Error boundaries/concepts Controlled forms Validation Touched/errors Reusable fields Schema validation concepts Local State Lifted State Context Redux Toolkit Zustand concepts Caching Invalidation Refetching Optimistic updates Fetch Axios awareness Loading Errors Retries Cancellation concepts Pagination Search Rendering Unnecessary rerenders Memoization Lazy loading Code splitting Bundle size Virtualization concepts Semantics Labels Keyboard navigation Focus Accessible forms ARIA awareness XSS Unsafe HTML Authentication UI Token-storage risks Secure cookies Dependency security Home Product listing Product detail Cart Login Profile Responsive UI Node runtime V8 Modules Npm Package.json Environment variables ECMAScript modules CommonJS awareness Import/export Module resolution Event loop Asynchronous I/O Promises Blocking vs non-blocking Fs Paths Streams Buffers File processing Readable Writable Transform Backpressure Application Routers Middleware Error middleware Express Middleware Api Architecture Resource modeling Status codes Filtering Sorting Versioning Idempotency Api Error Design Body Params Query Headers Zod concepts Joi concepts Databases Collections Documents BSON ObjectId CRUD Embed Reference How is data accessed? How often does it change? How large can it grow? Does it require independent lifecycle? Schema Model Middleware/hooks Methods References Single-field indexes Compound indexes Unique indexes Text/search awareness TTL indexes Query patterns Indexes Projection Explain-plan concepts $match $project $group $sort $lookup $unwind $facet Monthly revenue Top products Repeat customers Category performance Mongodb Transactions Replication Replica sets Sharding Shard keys Availability Managed clusters Security Connection configuration Backup concepts Monitoring Network access Session-Based Token-Based JWT OAuth2/OIDC concepts Password hashing Salt concepts Secure password reset Account enumeration risks Access token Refresh token Claims Expiration Rotation Revocation concepts Rbac Object-Level Authorization External identity Authorization code PKCE Scopes Social login concepts CSRF NoSQL injection Broken authorization Authentication attacks CORS Rate limiting Secret exposure Dependency risks Malicious file uploads Registration Email verification Refresh tokens Password reset RBAC Audit history Key/value TTL Session concepts Temporary state Cache-Aside Without Cache Cache Hit Email PDF reports Imports Exports Image processing Notifications BullMQ concepts Redis-backed jobs Queue Worker Retry Scheduling Idempotent Jobs Signature verification Replay protection Duplicate webhook delivery Multipart uploads File validation MIME validation Maximum size Malware-scanning concepts Storage separation Profile images Live chat Online status Agents Customers Rooms Messages Typing state Notification Job progress AI responses Feeds Full Stack Integration Login UI Session/token refresh Logout User state Api Cors Design Company A Company B Unit Testing Integration Testing API Testing Component Testing End-to-End Testing Services Utility functions Domain rules Auth DB behavior Component tests Behavior-based testing User interactions API mocking concepts Playwright concepts ESLint Formatting Type checks Naming Code review Clean architecture Blocking event loop CPU-bound work Async I/O Worker threads concepts Blocking code CPU workload Worker threads Background workers Architectural separation Missing indexes Large documents Unbounded queries Expensive aggregation Offset Pagination Cursor Pagination P50 P95 P99 Throughput Error rate Fixed window Sliding window concepts Token bucket concepts Redis-backed rate limiting Modular monolith first Service boundaries Independent deployment Database ownership Distributed-system complexity Node Microservices REST Queues Webhooks Kafka RabbitMQ AWS SQS Producer Consumer Dead-letter queues Timeout Exponential backoff Circuit breaker concepts Bulkhead concepts Controllers Providers Dependency injection Decorators Structured Node backend architecture Logging Logs Metrics Traces Request rate Latency DB latency Cache hits Queue depth Trace Span Context propagation Release Stack trace Environment Affected user/session correlation without oversharing sensitive data Images Containers Dockerfile Multi-stage builds Networking Volumes Docker Compose Filesystem Permissions Processes Ports Network commands concepts IAM EC2 S3 CloudWatch Load balancer DNS concepts Mongodb Atlas + Aws Aws Deployment Lambda API Gateway Event-driven workloads Ci/Cd Github Actions Configurations Secrets Rolling Blue/green concepts Canary concepts Rollback Pods Deployments ConfigMaps Health probes Scaling API Application Services Domain Database/Infrastructure Service Factory Strategy Adapter Observer Dependency Injection concepts Low-Level Design URL Shortener E-Commerce Platform Chat System Food Delivery Course Platform Ticket Booking Notification Service File Upload Service Social Feed SaaS Platform LLM API basics Streaming Structured responses AI chat interface Tool-call concepts Embeddings awareness RAG fundamentals Prompt injection awareness Unauthorized document access Rate limits Cost controls Output validation Secret protection