Server-Sent Events (SSE)

You can use Edge Functions to create a long-running service that can stream data to the browser using Server-Sent Events (SSE). While there is a 50ms limit on CPU time, time spent waiting for a response from an upstream service, or waiting for a timer to expire, does not count towards this limit. This means you can create a long-running service that can stream data to the browser.

import type { Context } from "@netlify/edge-functions";

export default async (request: Request, context: Context) => {
  let index = 0
  const encoder = new TextEncoder();
  const body = new ReadableStream({
    start(controller) {
      setInterval(() => {
        controller.enqueue(encoder.encode(`data: Hi ${index++}\n\n`));
      }, 1000);
    },
  });
  return new Response(body, {
    headers: {
      "Content-Type": "text/event-stream",
    },
  });
};

See this in action

• View the response from the Edge Function
• The Edge Function code: sse.ts

Pro tip!

Need to wait a long time before starting to stream a response? Check out the slow streaming example.