Web Development

Websockets vs AJAX

  • Long-polling
    • Let’s say you want to check automatically if there is a new comment to add it automatically at the bottom of an article.
    • Long-polling means you would check every Х seconds if there is something new, with web-sockets comments can come in automatically as they are posted
  • Websockets have two advantages.
    • They have much less overhead, which results in a better network performance
    • They allow the server to send data that the client hasn’t explicitly requested.
    • The second one is the most important advantage.
  • In AJAX, everything the server sends must be the response to a previous request by the client, and every request can only be answered once.
    • But in many applications, especially multi-user applications, events happen on the server and these events must be pushed to the clients immediately.
    • There are workarounds for that in AJAX, like delaying the answer to a request until there is something to report (long-polling), but these are quite dirty.
    • That’s why there are WebSockets.
    • With a WebSocket connection, the server can send messages to the clients when it wants and as often as it wants, without having to wait for a request from the client.
  • But unfortunately, WebSockets also have disadvantages:
    • They aren’t as well-supported by web development frameworks
      • yet
    • Not all web browsers support it
      • but most desktop browsers already do
    • Many proxies and reverse-proxies can’t relay WebSocket traffic
      • yet


  • Websockets are a powerful technology and could certainly cater to the limited use cases but there can be compatibility problems with older browsers and network intermediaries.
  • In fact, some folks even recommend having an HTTP fallback in case Websockets isn’t supported.
  • Unless you have requirements that necessitate WebSockets, such as full-duplex bi-directional communications, for example, you might be better off using existing AJAX-based solutions.
  • If you have requirements to push notifications to your user interface, WebSockets can be a good idea, but if you are literally looking for form submission and auto-complete, then these problems have already been solved using Ajax