Data & APIs

Why this stage matters

Most frontend work is moving data between a server and a screen. Doing it well means handling every state (loading, error, empty, stale), caching sensibly, and knowing which protocol fits which problem.

What to learn

1. Must know

   REST & HTTP Caching

   Mark as done

   Resource design, pagination, error formats, and caching headers (Cache-Control, ETag) that make apps fast for free.

   You're done when

   • You can read an API's docs and integrate it with full error handling.
   • You know what Cache-Control: no-cache actually means.

   Resources

   • MDN — HTTP cachingDocs
2. Optional

   GraphQL

   Mark as done

   Queries, mutations, fragments, and client caching with Apollo or urql. Learn it when your company uses it.

   You're done when

   • You can write a query with fragments and variables.

   Resources

   • graphql.org — LearnDocs
3. Learn next

   Real-time & Streaming

   Mark as done

   WebSockets for two-way messaging, Server-Sent Events for server push, and streamed responses, which power AI chat interfaces.

   You're done when

   • You can render a streamed response token by token.
   • You know when SSE is enough and when you need WebSockets.

   Resources

   • MDN — Server-sent eventsDocs
   • MDN — Streams APIDocs

Common mistakes

• Showing a blank screen when a request fails. Every request has four states; design all of them.
• Fetching the same data in five components instead of caching it once.