diff --git a/client.js b/client.js
index 1a8a5f1..ddc345e 100644
--- a/client.js
+++ b/client.js
@@ -1,21 +1,16 @@
-module.exports = Client
+const { Buffer } = require('safe-buffer')
+const debug = require('debug')('bittorrent-tracker:client')
+const EventEmitter = require('events')
+const once = require('once')
+const parallel = require('run-parallel')
+const Peer = require('simple-peer')
+const uniq = require('uniq')
+const url = require('url')
 
-var Buffer = require('safe-buffer').Buffer
-var debug = require('debug')('bittorrent-tracker:client')
-var EventEmitter = require('events').EventEmitter
-var inherits = require('inherits')
-var once = require('once')
-var parallel = require('run-parallel')
-var Peer = require('simple-peer')
-var uniq = require('uniq')
-var url = require('url')
-
-var common = require('./lib/common')
-var HTTPTracker = require('./lib/client/http-tracker') // empty object in browser
-var UDPTracker = require('./lib/client/udp-tracker') // empty object in browser
-var WebSocketTracker = require('./lib/client/websocket-tracker')
-
-inherits(Client, EventEmitter)
+const common = require('./lib/common')
+const HTTPTracker = require('./lib/client/http-tracker') // empty object in browser
+const UDPTracker = require('./lib/client/udp-tracker') // empty object in browser
+const WebSocketTracker = require('./lib/client/websocket-tracker')
 
 /**
  * BitTorrent tracker client.
@@ -32,86 +27,203 @@ inherits(Client, EventEmitter)
  * @param {number} opts.userAgent                User-Agent header for http requests
  * @param {number} opts.wrtc                     custom webrtc impl (useful in node.js)
  */
-function Client (opts) {
-  var self = this
-  if (!(self instanceof Client)) return new Client(opts)
-  EventEmitter.call(self)
-  if (!opts) opts = {}
+class Client extends EventEmitter {
+  constructor (opts = {}) {
+    super()
 
-  if (!opts.peerId) throw new Error('Option `peerId` is required')
-  if (!opts.infoHash) throw new Error('Option `infoHash` is required')
-  if (!opts.announce) throw new Error('Option `announce` is required')
-  if (!process.browser && !opts.port) throw new Error('Option `port` is required')
+    if (!opts.peerId) throw new Error('Option `peerId` is required')
+    if (!opts.infoHash) throw new Error('Option `infoHash` is required')
+    if (!opts.announce) throw new Error('Option `announce` is required')
+    if (!process.browser && !opts.port) throw new Error('Option `port` is required')
 
-  self.peerId = typeof opts.peerId === 'string'
-    ? opts.peerId
-    : opts.peerId.toString('hex')
-  self._peerIdBuffer = Buffer.from(self.peerId, 'hex')
-  self._peerIdBinary = self._peerIdBuffer.toString('binary')
+    this.peerId = typeof opts.peerId === 'string'
+      ? opts.peerId
+      : opts.peerId.toString('hex')
+    this._peerIdBuffer = Buffer.from(this.peerId, 'hex')
+    this._peerIdBinary = this._peerIdBuffer.toString('binary')
 
-  self.infoHash = typeof opts.infoHash === 'string'
-    ? opts.infoHash.toLowerCase()
-    : opts.infoHash.toString('hex')
-  self._infoHashBuffer = Buffer.from(self.infoHash, 'hex')
-  self._infoHashBinary = self._infoHashBuffer.toString('binary')
+    this.infoHash = typeof opts.infoHash === 'string'
+      ? opts.infoHash.toLowerCase()
+      : opts.infoHash.toString('hex')
+    this._infoHashBuffer = Buffer.from(this.infoHash, 'hex')
+    this._infoHashBinary = this._infoHashBuffer.toString('binary')
 
-  debug('new client %s', self.infoHash)
+    debug('new client %s', this.infoHash)
 
-  self.destroyed = false
+    this.destroyed = false
 
-  self._port = opts.port
-  self._getAnnounceOpts = opts.getAnnounceOpts
-  self._rtcConfig = opts.rtcConfig
-  self._userAgent = opts.userAgent
+    this._port = opts.port
+    this._getAnnounceOpts = opts.getAnnounceOpts
+    this._rtcConfig = opts.rtcConfig
+    this._userAgent = opts.userAgent
 
-  // Support lazy 'wrtc' module initialization
-  // See: https://github.com/webtorrent/webtorrent-hybrid/issues/46
-  self._wrtc = typeof opts.wrtc === 'function' ? opts.wrtc() : opts.wrtc
+    // Support lazy 'wrtc' module initialization
+    // See: https://github.com/webtorrent/webtorrent-hybrid/issues/46
+    this._wrtc = typeof opts.wrtc === 'function' ? opts.wrtc() : opts.wrtc
 
-  var announce = typeof opts.announce === 'string'
-    ? [ opts.announce ]
-    : opts.announce == null ? [] : opts.announce
+    let announce = typeof opts.announce === 'string'
+      ? [ opts.announce ]
+      : opts.announce == null ? [] : opts.announce
 
-  // Remove trailing slash from trackers to catch duplicates
-  announce = announce.map(function (announceUrl) {
-    announceUrl = announceUrl.toString()
-    if (announceUrl[announceUrl.length - 1] === '/') {
-      announceUrl = announceUrl.substring(0, announceUrl.length - 1)
+    // Remove trailing slash from trackers to catch duplicates
+    announce = announce.map(announceUrl => {
+      announceUrl = announceUrl.toString()
+      if (announceUrl[announceUrl.length - 1] === '/') {
+        announceUrl = announceUrl.substring(0, announceUrl.length - 1)
+      }
+      return announceUrl
+    })
+    announce = uniq(announce)
+
+    const webrtcSupport = this._wrtc !== false && (!!this._wrtc || Peer.WEBRTC_SUPPORT)
+
+    const nextTickWarn = err => {
+      process.nextTick(() => {
+        this.emit('warning', err)
+      })
     }
-    return announceUrl
-  })
-  announce = uniq(announce)
 
-  var webrtcSupport = self._wrtc !== false && (!!self._wrtc || Peer.WEBRTC_SUPPORT)
-
-  self._trackers = announce
-    .map(function (announceUrl) {
-      var protocol = url.parse(announceUrl).protocol
-      if ((protocol === 'http:' || protocol === 'https:') &&
-          typeof HTTPTracker === 'function') {
-        return new HTTPTracker(self, announceUrl)
-      } else if (protocol === 'udp:' && typeof UDPTracker === 'function') {
-        return new UDPTracker(self, announceUrl)
-      } else if ((protocol === 'ws:' || protocol === 'wss:') && webrtcSupport) {
-        // Skip ws:// trackers on https:// sites because they throw SecurityError
-        if (protocol === 'ws:' && typeof window !== 'undefined' &&
-            window.location.protocol === 'https:') {
-          nextTickWarn(new Error('Unsupported tracker protocol: ' + announceUrl))
+    this._trackers = announce
+      .map(announceUrl => {
+        const protocol = url.parse(announceUrl).protocol
+        if ((protocol === 'http:' || protocol === 'https:') &&
+            typeof HTTPTracker === 'function') {
+          return new HTTPTracker(this, announceUrl)
+        } else if (protocol === 'udp:' && typeof UDPTracker === 'function') {
+          return new UDPTracker(this, announceUrl)
+        } else if ((protocol === 'ws:' || protocol === 'wss:') && webrtcSupport) {
+          // Skip ws:// trackers on https:// sites because they throw SecurityError
+          if (protocol === 'ws:' && typeof window !== 'undefined' &&
+              window.location.protocol === 'https:') {
+            nextTickWarn(new Error(`Unsupported tracker protocol: ${announceUrl}`))
+            return null
+          }
+          return new WebSocketTracker(this, announceUrl)
+        } else {
+          nextTickWarn(new Error(`Unsupported tracker protocol: ${announceUrl}`))
           return null
         }
-        return new WebSocketTracker(self, announceUrl)
-      } else {
-        nextTickWarn(new Error('Unsupported tracker protocol: ' + announceUrl))
-        return null
-      }
-    })
-    .filter(Boolean)
+      })
+      .filter(Boolean)
+  }
 
-  function nextTickWarn (err) {
-    process.nextTick(function () {
-      self.emit('warning', err)
+  /**
+   * Send a `start` announce to the trackers.
+   * @param {Object} opts
+   * @param {number=} opts.uploaded
+   * @param {number=} opts.downloaded
+   * @param {number=} opts.left (if not set, calculated automatically)
+   */
+  start (opts) {
+    debug('send `start`')
+    opts = this._defaultAnnounceOpts(opts)
+    opts.event = 'started'
+    this._announce(opts)
+
+    // start announcing on intervals
+    this._trackers.forEach(tracker => {
+      tracker.setInterval()
     })
   }
+
+  /**
+   * Send a `stop` announce to the trackers.
+   * @param {Object} opts
+   * @param {number=} opts.uploaded
+   * @param {number=} opts.downloaded
+   * @param {number=} opts.numwant
+   * @param {number=} opts.left (if not set, calculated automatically)
+   */
+  stop (opts) {
+    debug('send `stop`')
+    opts = this._defaultAnnounceOpts(opts)
+    opts.event = 'stopped'
+    this._announce(opts)
+  }
+
+  /**
+   * Send a `complete` announce to the trackers.
+   * @param {Object} opts
+   * @param {number=} opts.uploaded
+   * @param {number=} opts.downloaded
+   * @param {number=} opts.numwant
+   * @param {number=} opts.left (if not set, calculated automatically)
+   */
+  complete (opts) {
+    debug('send `complete`')
+    if (!opts) opts = {}
+    opts = this._defaultAnnounceOpts(opts)
+    opts.event = 'completed'
+    this._announce(opts)
+  }
+
+  /**
+   * Send a `update` announce to the trackers.
+   * @param {Object} opts
+   * @param {number=} opts.uploaded
+   * @param {number=} opts.downloaded
+   * @param {number=} opts.numwant
+   * @param {number=} opts.left (if not set, calculated automatically)
+   */
+  update (opts) {
+    debug('send `update`')
+    opts = this._defaultAnnounceOpts(opts)
+    if (opts.event) delete opts.event
+    this._announce(opts)
+  }
+
+  _announce (opts) {
+    this._trackers.forEach(tracker => {
+      // tracker should not modify `opts` object, it's passed to all trackers
+      tracker.announce(opts)
+    })
+  }
+
+  /**
+   * Send a scrape request to the trackers.
+   * @param {Object} opts
+   */
+  scrape (opts) {
+    debug('send `scrape`')
+    if (!opts) opts = {}
+    this._trackers.forEach(tracker => {
+      // tracker should not modify `opts` object, it's passed to all trackers
+      tracker.scrape(opts)
+    })
+  }
+
+  setInterval (intervalMs) {
+    debug('setInterval %d', intervalMs)
+    this._trackers.forEach(tracker => {
+      tracker.setInterval(intervalMs)
+    })
+  }
+
+  destroy (cb) {
+    if (this.destroyed) return
+    this.destroyed = true
+    debug('destroy')
+
+    const tasks = this._trackers.map(tracker => cb => {
+      tracker.destroy(cb)
+    })
+
+    parallel(tasks, cb)
+
+    this._trackers = []
+    this._getAnnounceOpts = null
+  }
+
+  _defaultAnnounceOpts (opts = {}) {
+    if (opts.numwant == null) opts.numwant = common.DEFAULT_ANNOUNCE_PEERS
+
+    if (opts.uploaded == null) opts.uploaded = 0
+    if (opts.downloaded == null) opts.downloaded = 0
+
+    if (this._getAnnounceOpts) opts = Object.assign({}, opts, this._getAnnounceOpts())
+
+    return opts
+  }
 }
 
 /**
@@ -123,30 +235,30 @@ function Client (opts) {
  * @param  {string} opts.announce
  * @param  {function} cb
  */
-Client.scrape = function (opts, cb) {
+Client.scrape = (opts, cb) => {
   cb = once(cb)
 
   if (!opts.infoHash) throw new Error('Option `infoHash` is required')
   if (!opts.announce) throw new Error('Option `announce` is required')
 
-  var clientOpts = Object.assign({}, opts, {
+  const clientOpts = Object.assign({}, opts, {
     infoHash: Array.isArray(opts.infoHash) ? opts.infoHash[0] : opts.infoHash,
     peerId: Buffer.from('01234567890123456789'), // dummy value
     port: 6881 // dummy value
   })
 
-  var client = new Client(clientOpts)
+  const client = new Client(clientOpts)
   client.once('error', cb)
   client.once('warning', cb)
 
-  var len = Array.isArray(opts.infoHash) ? opts.infoHash.length : 1
-  var results = {}
-  client.on('scrape', function (data) {
+  let len = Array.isArray(opts.infoHash) ? opts.infoHash.length : 1
+  const results = {}
+  client.on('scrape', data => {
     len -= 1
     results[data.infoHash] = data
     if (len === 0) {
       client.destroy()
-      var keys = Object.keys(results)
+      const keys = Object.keys(results)
       if (keys.length === 1) {
         cb(null, results[keys[0]])
       } else {
@@ -156,7 +268,7 @@ Client.scrape = function (opts, cb) {
   })
 
   opts.infoHash = Array.isArray(opts.infoHash)
-    ? opts.infoHash.map(function (infoHash) {
+    ? opts.infoHash.map(infoHash => {
       return Buffer.from(infoHash, 'hex')
     })
     : Buffer.from(opts.infoHash, 'hex')
@@ -164,132 +276,4 @@ Client.scrape = function (opts, cb) {
   return client
 }
 
-/**
- * Send a `start` announce to the trackers.
- * @param {Object} opts
- * @param {number=} opts.uploaded
- * @param {number=} opts.downloaded
- * @param {number=} opts.left (if not set, calculated automatically)
- */
-Client.prototype.start = function (opts) {
-  var self = this
-  debug('send `start`')
-  opts = self._defaultAnnounceOpts(opts)
-  opts.event = 'started'
-  self._announce(opts)
-
-  // start announcing on intervals
-  self._trackers.forEach(function (tracker) {
-    tracker.setInterval()
-  })
-}
-
-/**
- * Send a `stop` announce to the trackers.
- * @param {Object} opts
- * @param {number=} opts.uploaded
- * @param {number=} opts.downloaded
- * @param {number=} opts.numwant
- * @param {number=} opts.left (if not set, calculated automatically)
- */
-Client.prototype.stop = function (opts) {
-  var self = this
-  debug('send `stop`')
-  opts = self._defaultAnnounceOpts(opts)
-  opts.event = 'stopped'
-  self._announce(opts)
-}
-
-/**
- * Send a `complete` announce to the trackers.
- * @param {Object} opts
- * @param {number=} opts.uploaded
- * @param {number=} opts.downloaded
- * @param {number=} opts.numwant
- * @param {number=} opts.left (if not set, calculated automatically)
- */
-Client.prototype.complete = function (opts) {
-  var self = this
-  debug('send `complete`')
-  if (!opts) opts = {}
-  opts = self._defaultAnnounceOpts(opts)
-  opts.event = 'completed'
-  self._announce(opts)
-}
-
-/**
- * Send a `update` announce to the trackers.
- * @param {Object} opts
- * @param {number=} opts.uploaded
- * @param {number=} opts.downloaded
- * @param {number=} opts.numwant
- * @param {number=} opts.left (if not set, calculated automatically)
- */
-Client.prototype.update = function (opts) {
-  var self = this
-  debug('send `update`')
-  opts = self._defaultAnnounceOpts(opts)
-  if (opts.event) delete opts.event
-  self._announce(opts)
-}
-
-Client.prototype._announce = function (opts) {
-  var self = this
-  self._trackers.forEach(function (tracker) {
-    // tracker should not modify `opts` object, it's passed to all trackers
-    tracker.announce(opts)
-  })
-}
-
-/**
- * Send a scrape request to the trackers.
- * @param {Object} opts
- */
-Client.prototype.scrape = function (opts) {
-  var self = this
-  debug('send `scrape`')
-  if (!opts) opts = {}
-  self._trackers.forEach(function (tracker) {
-    // tracker should not modify `opts` object, it's passed to all trackers
-    tracker.scrape(opts)
-  })
-}
-
-Client.prototype.setInterval = function (intervalMs) {
-  var self = this
-  debug('setInterval %d', intervalMs)
-  self._trackers.forEach(function (tracker) {
-    tracker.setInterval(intervalMs)
-  })
-}
-
-Client.prototype.destroy = function (cb) {
-  var self = this
-  if (self.destroyed) return
-  self.destroyed = true
-  debug('destroy')
-
-  var tasks = self._trackers.map(function (tracker) {
-    return function (cb) {
-      tracker.destroy(cb)
-    }
-  })
-
-  parallel(tasks, cb)
-
-  self._trackers = []
-  self._getAnnounceOpts = null
-}
-
-Client.prototype._defaultAnnounceOpts = function (opts) {
-  var self = this
-  if (!opts) opts = {}
-
-  if (opts.numwant == null) opts.numwant = common.DEFAULT_ANNOUNCE_PEERS
-
-  if (opts.uploaded == null) opts.uploaded = 0
-  if (opts.downloaded == null) opts.downloaded = 0
-
-  if (self._getAnnounceOpts) opts = Object.assign({}, opts, self._getAnnounceOpts())
-  return opts
-}
+module.exports = Client
diff --git a/index.js b/index.js
index 1f79a6e..1e7f2a4 100644
--- a/index.js
+++ b/index.js
@@ -1,5 +1,5 @@
-var Client = require('./client')
-var Server = require('./server')
+const Client = require('./client')
+const Server = require('./server')
 
 module.exports = Client
 module.exports.Client = Client