Edge Functions Examples / Server-Sent Events (SSE)

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

Pro tip!

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

Explore more examples

What are Edge Functions?

Using JavaScript and TypeScript, Netlify Edge Functions give you the power to modify network requests to localize content, serve relevant ads, authenticate visitors, A/B test content, and much more! And this all happens at the Edge — directly from the worldwide location closest to each user.

To use Edge Functions on Netlify, add JavaScript or TypeScript files to an edge-functions directory in your project.

Learn more in the docs.

Deploy this site to Netlify

Try out Edge Functions on Netlify today! Click the button below to deploy this site with all of its demos to your Netlify account.

Deploy to Netlify