The Server-Sent Events specification describes a built-in class EventSource, that keeps connection with the server and allows to receive events from it.
Similar to WebSocket, the connection is persistent.
But there are several important differences:
| WebSocket | EventSource |
|---|---|
| Bi-directional: both client and server can exchange messages | One-directional: only server sends data |
| Binary and text data | Only text |
| WebSocket protocol | Regular HTTP |
EventSource is a less-powerful way of communicating with the server than WebSocket.
Why should one ever use it?
The main reason: it’s simpler. In many applications, the power of WebSocket is a little bit too much.
We need to receive a stream of data from server: maybe chat messages or market prices, or whatever. That’s what EventSource is good at. Also it supports auto-reconnect, something we need to implement manually with WebSocket. Besides, it’s a plain old HTTP, not a new protocol.
- Step-1
npm install
- Step-2
npm start
- Step-3: Open below url in the browser
http://localhost:5000