discord-message-listener.js

const WebSocket = require('ws');
require('dotenv').config();

// Websocket instance
const ws = new WebSocket('wss://gateway.discord.gg/?v=9&encoding=json');

// Heartbeat interval
const heartBit = (interval) => {
  setTimeout(() => {
    ws.send(JSON.stringify({
      op: 1,
      d: null
    }));
  }, interval);
}

// Websocket event listeners
// Connection Open
ws.on('open', () => {
  ws.send(JSON.stringify({
    op: 2,
    d: {
      token: process.env.AUTH_TOKEN,
      capabilities: 253,
      properties: {
        "os": "Linux",
        "browser": "Chrome",
        "device": "Linux"
      }
    }
  }))
})

// Getting Responses
ws.on('message', (data) => {
  let res = JSON.parse(data);
  let { op, d, t } = res;

  switch (op) {
    case 10:
      let { heartbeat_interval } = d;
      heartBit(heartbeat_interval);
      break;
    case 11:
      console.log(`[${t}]`, 'Recieved heartbeat');
  }

  switch (t) {
    case 'READY':
      console.log(`Logged in as ${d.user.username}#${d.user.discriminator}`);
      break

    case 'MESSAGE_CREATE':
      let author = d.author.username;
      let authorId = d.author.id;
      let content = d.content;

      console.log(`[${author}] ${content}`);
  }
})