API Design & Data Fetching

Every frontend system design answer eventually reaches the API layer. Interviewers want contract literacy plus resilience: what the endpoint looks like, and what your UI does when it is slow, flaky, or answers out of order.

This module covers REST resource design, GraphQL trade-offs, versioning strategies, idempotency, and the two pagination models, then moves into the client patterns that actually break in production.

You will learn retry with exponential backoff and jitter, timeout budgets, AbortController-based cancellation, debounce vs throttle, polling vs push, and the three standard fixes for autocomplete race conditions.

The canonical drill is Google-style search autocomplete: input → debounce → request → cache → results, with stale responses discarded rather than rendered.

Phase 4 (Week 4) of the interview roadmap. Senior Track spans modules 1–19; the Staff Track starts at module 20.