Programming Tutorials

  You have set up your Next.js 15 application, configured your LangChain chains, and everything works perfectly in the console. But when you connect it to your React frontend, the application hangs. The user stares at a loading spinner for five seconds, and then the entire response snaps into existence at once. This destroys the User Experience. The "magic" of LLMs lies in the  token-by-token streaming effect —the typewriter illusion that makes the AI feel alive and responsive. Achieving this in the App Router is surprisingly difficult. You are battling three adversaries: the serialization boundary between React Server Components (RSC) and the client, the mismatch between LangChain’s async iterables and standard Web Streams, and the strict typing of TypeScript. This guide provides a production-grade, rigorous solution to implement real-time streaming using Next.js 15 Route Handlers and LangChain. The Root Cause: Why Streaming Breaks To fix the problem, we must understand the ...