Edge Runtime uses a lightweight V8 isolate close to users. Node.js runtime offers full APIs for database drivers and file system access.
Common Interview Questions
Q: How to select runtime?
Answer: Set per route handler, middleware, or page. Edge for low-latency geo-personalization; Node for heavy compute and native modules.
export const runtime = "edge"; // or "nodejs" (default)
Q: Edge limitations?
Answer: No Node fs/net APIs, limited npm packages (no native addons), smaller memory/cpu caps. Use fetch, Web Crypto, and edge-compatible DB drivers.
Q: When prefer Edge?
Answer: Middleware, A/B testing, geo routing, auth token verification, and read-heavy APIs with edge-compatible data (Vercel KV, D1, Upstash).
Q: Cold start differences?
Answer: Edge isolates start faster than Node serverless functions — discuss latency vs compatibility trade-off for global users.
Key Points for Interviews
-
Edge = Web APIs subset, globally distributed
-
Node = default, full ecosystem compatibility
-
Middleware always Edge
-
Check library edge compatibility before deploying
-
Measure — Edge is not automatically faster for DB-heavy work