---
title: "Discussion on \"Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub\" | Hashnode"
description: "Discussion on \"Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub\". How does WhatsApp deliver a message almost instantly?\nYou send a message.\nA second later, the other person gets it.\nThere is no refresh button.\nYou don't sit there thinking:\n\n“Let me refresh the page"
url: "https://hashnode.com/posts/realtime-systems-polling-websockets-sse-and-pub-sub/6a8f26879736b30a59cd1f66"
---

[Feed](https://hashnode.com/feed) /

Discussion

# [Realtime Systems: Polling, WebSockets, SSE, and Pub/Sub](https://devwithsahil.hashnode.dev/realtime-systems-polling-websockets-sse-and-pub-sub?utm_source=hashnode&utm_medium=feed)

How does WhatsApp deliver a message almost instantly? You send a message. A second later, the other person gets it. There is no refresh button. You don't sit there thinking: “Let me refresh the page

Aug 26 · 18 min read · devwithsahil.hashnode.dev  
Read the article

-   [#chaicode](https://hashnode.com/tag/chaicode)
-   [#javascript](https://hashnode.com/tag/javascript)
-   [#web-sockets](https://hashnode.com/tag/web-sockets)

## Written by

[Sahil Prashar](https://hashnode.com/@sahilprashar)

@sahilprashar

  
[View profile](https://hashnode.com/@sahilprashar)

## Responses

Markdown supported · ⌘↵ to post

No responses yet.