AJAX & Async Requests·AJAX from first request to live updates

Polling and streaming

Choose polling, long polling or server-sent events for live data.

Beginner 13 min read Lesson 8 of 300 Challenge included

What you will be able to do

Poll on a sensible interval with backoff.
Use SSE for one-way updates.
Use WebSockets for two-way collaboration.
Cancel and reconnect deliberately.

In plain English

Polling asks repeatedly; long polling holds a request; server-sent events stream one-way messages. WebSockets are for two-way realtime. Pick the simplest model that meets the freshness requirement.

sse.jsJavaScript

const source = new EventSource('/api/events')
source.addEventListener('lesson', (event) => {
  const lesson = JSON.parse(event.data)
  console.log(lesson.title)
})
source.onerror = () => console.log('reconnecting')

Your turn

Open an event stream

Easy

Create an EventSource for /api/events.

JAVASCRIPT · starter

const source =

Check your understanding before moving on.

Knowledge checkQuestion 1

Which transport streams one-way updates from server to client?

Select an answer to continue

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Next: Caching and cancellation

Lesson 8 of 300 · 0% of course