I know how to send data to server, how to get data from server, but I don't understand how client knows when to send a request to server, to get the massage. I know that it doesn't ping it every second, but now I don't see any other way.

I will use React JS for the UI with node JS for the server part.

Thanks in advance. <3

CodePudding user response：

Imagine you have:

• A central server
• client1 (clt1) that sends the message
• client2 (clt2) that receives the message

When only clt1 is online and it sends a message:

• 1. Store the message of clt1 in the server.
• 2. When clt2 reconnects, it sends a request to the server to get the messages.

When both are online:

• 1. clt1 sends a message to the server.
• 2. As the server knows that clt2 is online, it immediatly sends the message to clt2.

When only only clt2 is online:

• 1. clt2 sends a request to the server to know if messages have been send for him/her.
• 2. If yes, get those.

It works only if the server knows at any moment if the clients are online or not.

Hope it helps