Soundcloud's follower-maze challenge in Javascript

maze.js

// This code could use comments, tests, & a million other things.. 
// but since I did not apply at soundcloud, it doesn't matter 

const net = require('net')
const split = require('split')
const PriorityQueue = require('priorityqueuejs')

const clients = {}
const followers = {}
const queue = new PriorityQueue((a, b) => b.sequence - a.sequence)

// QUEUE WORKER
const process = event => {
  const { type, from, to, payload } = event
  switch (type) {
    case 'F':
      if (to in clients) {
        followers[to].add(from)
        clients[to].write(payload + '\r\n')
      }
      break
    case 'U':
      if (to in followers) {
        followers[to].delete(from)
      }
      break
    case 'B':
      Object.keys(clients).forEach(id => {
        clients[id].write(payload + '\r\n')
      })
      break
    case 'P':
      if (to in clients) {
        clients[to].write(payload + '\r\n')
      }
      break
    case 'S':
      if (from in followers) {
        followers[from].forEach(followerId => {
          clients[followerId].write(payload + '\r\n')
        })
      }
      break
  }
}

let index = 1
const next = () => {
  if (!queue.isEmpty()) {
    const nextInQueue = queue.peek()
    const nextIndex = nextInQueue.sequence
    while (nextIndex == index) {
      process(queue.deq())
      index++
    }
    setImmediate(next)
  }
}

// EVENTS
net.createServer(socket => {
  socket.setEncoding('utf8')
  socket.pipe(split()).on('data', payload => {
    const [sequenceStr, type, from, to] = payload.split('|')
    const sequence = parseInt(sequenceStr, 10)
    if (!isNaN(sequence)) {
      if (queue.isEmpty()) {
        setImmediate(next)
      }
      queue.enq({ sequence, type, from, to, payload })
    }
  })
}).listen(9090)

// CLIENTS
net.createServer(client => {
  client.setEncoding('utf8')
  const stream = client.pipe(split())
  stream.once('data', id => {
    const clientId = id.toString()
    clients[clientId] = client
    followers[clientId] = new Set()
    console.log('registered', clientId)
    client.once('close', () => {
      console.log('deregistered', clientId)
      delete clients[clientId]
      delete followers[clientId]
    })
  })
}).listen(9099)