Example using home-assistant-js-websocket with Node

demo.js

const WebSocket = require('ws');
global.WebSocket = WebSocket;
const HAWS = require("home-assistant-js-websocket");

const getWsUrl = haUrl => `ws://${haUrl}/api/websocket`;

HAWS.createConnection(getWsUrl('localhost:8123')).then(conn => {
  HAWS.subscribeEntities(conn, logEntities);
});

function logEntities(entities) {
  Object.keys(entities).forEach(key => console.log(`${key}: ${entities[key].state}`));
  console.log('')
}