WebSockets with socket.io

JavaScript lib for WebSockets
Socket.IO

Socket.IO — Chat | Socket.IO (example app)

Socket.IO — Docs | Socket.IO

Source:

socketio/socket.io: Realtime application framework (Node.JS server) @ GitHub

socketio/socket.io-client: Realtime application framework (client) @ GitHub

socket.io/examples at master · socketio/socket.io

Download:
samples-server/s/websocket-chat at master · mdn/samples-server

simple JS client/server chat, without other libraries

socket.io - npm

socket.io-client - npm

engine.io - npm
The realtime engine behind Socket.IO. Provides the foundation of a bidirectional connection between client and server

Alternative library for node.js
express-ws - npm

8 Node.js Web Socket Libraries for 2019 – Bits and Pieces

Other languages support:

googollee/go-socket.io: socket.io library for golang, a realtime application framework.
socket.io library for golang, a realtime application framework.
WebSockets support in ASP.NET Core | Microsoft Docs

More docs:

The WebSocket API (WebSockets) - Web APIs | MDN