Frontend Backend Integration Through APIs Questions

Understanding how frontend components interact with backend APIs using HTTP requests (fetch, axios, etc.), handling asynchronous responses and errors, managing data flow from API responses to UI updates. Ability to design APIs that frontend needs and implement corresponding client-side code to consume them properly.

EasyTechnical

44 practiced

Explain how Cross-Origin Resource Sharing (CORS) works when your frontend served from https://app.example.com calls a backend API at https://api.example.com. Describe what triggers a preflight (OPTIONS) request, which response headers the server must return to permit the request (including credentialed requests), and step-by-step debugging techniques you would use when the browser reports CORS errors in the console.

HardTechnical

48 practiced

A GraphQL server is experiencing N+1 query problems and is vulnerable to expensive nested queries that exhaust resources. Propose concrete server-side mitigations: DataLoader or batching, query depth/complexity limiting, persisted queries, query whitelisting, caching resolver results, timeouts, and monitoring. Explain how you'd measure query cost and enforce limits without breaking useful client queries.

EasyTechnical

42 practiced

Compare session cookie-based authentication and token-based (JWT) authentication for single-page applications (SPAs). As a full-stack developer, discuss security trade-offs (XSS and CSRF), cross-origin requests, storage considerations on the client, and recommend a secure approach for a modern SPA with both web and mobile clients.

MediumTechnical

48 practiced

You must introduce a breaking change to an existing public REST API used by many frontends. Compare URI-based versioning (e.g., /v2/), header-based versioning (Accept header), and content negotiation. Propose a concrete deprecation and rollout plan that minimizes disruption, including timelines, compatibility layers, communication strategies, and how you would enforce and monitor migration progress.

MediumTechnical

53 practiced

Set up a consumer-driven contract-testing workflow between a React frontend and an Express backend (or equivalent) using Pact or a similar tool. Describe how consumer tests are authored, how contracts are published and validated by the provider in CI, how the frontend team uses mock provider responses locally, and strategies to version and evolve contracts without breaking consumers.

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