Implement real-time communication between multiple clients and a server.
With HTTP requests, the server cannot initiate a request to the client (browser). ie HTTP requests are always initiated by the client (browser). This means we cannot push data to the client easily. HTTP requests are not persistent. They are transactional.
Q: Can we accomplish real time updates without a persistent conn? (ie without WebSockets?)
A: Yes, with polling. We can use setInterval or setTimeout for this.
- Overhead: A lot of HTTP requests (headers, body, cookies, etc)
- Not truly real time: every 5s or 1s or wtv.
- Complex error handling needed
- When polling, can you do other stuff?
- Request deltas
Q: Any other (better) solutions?
A: Long polling "Comet"
One connection (singleton) that stays hanging b/c the server doesn't respond until it has a new message (payload) for that client.
Instead of http:// a connection is established via ws://
Like with any TCP connection, the underlying library (browser) has to support a bunch of events/triggers:
- open
- send
- receive
- close
This demo and the code for it was taken from Fabio (Toronto instructor).
You can see his lecture notes and code here: https://github.com/fzero/lhl-lectures/tree/master/w5d3-websockets. Thanks Fabio!