const SteamUser = require('steam-user') // npm install steam-user

const MSG = `Default message.`
const ACCOUNT = {
  accountName: '',
  password: ''
}

let client = new SteamUser()

client.logOn(ACCOUNT)

client.on('loggedOn', details => {
  console.log(`Logged on with ${client.steamID.getSteamID64()}.`)

  client.setPersona(SteamUser.EPersonaState.Online)

  client.on('friendMessage', (id, msg) => {
    console.log(`${id.getSteamID64()}: ${msg}`)

    client.chatMessage(id, MSG)
  })

  client.on('error', (err) => console.log(`Error: ${err.message}.`))
})