diff --git a/.eslintrc b/.eslintrc
index 294ee6c..da143a7 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -1,5 +1,11 @@
 root: true
 
+parserOptions:
+  ecmaVersion: 2017
+
+env:
+  node: true
+
 rules:
   accessor-pairs: [2]
   array-bracket-newline: [0]
@@ -182,7 +188,7 @@ rules:
   no-useless-concat: [2]
   no-useless-constructor: [2]
   no-useless-escape: [2]
-  no-var: [0]
+  no-var: [2]
   no-warning-comments: [0]
   no-whitespace-before-property: [2]
   no-with: [2]
@@ -221,7 +227,7 @@ rules:
   space-infix-ops: [2]
   space-unary-ops: [2]
   spaced-comment: [2, always, {markers: ["!"]}]
-  strict: [0]
+  strict: [2]
   switch-colon-spacing: [2]
   symbol-description: [2]
   template-curly-spacing: [2, never]
@@ -233,6 +239,3 @@ rules:
   wrap-regex: [0]
   yield-star-spacing: [2, {before: true, after: false}]
   yoda: [2, never]
-
-env:
-  node: true
diff --git a/example.js b/example.js
index 7d07820..0b96397 100644
--- a/example.js
+++ b/example.js
@@ -1,9 +1,11 @@
-var packet = require('./')
-var dgram = require('dgram')
+'use strict'
 
-var socket = dgram.createSocket('udp4')
+const packet = require('./')
+const dgram = require('dgram')
 
-var buf = packet.encode({
+const socket = dgram.createSocket('udp4')
+
+const buf = packet.encode({
   type: 'query',
   id: 1,
   flags: packet.RECURSION_DESIRED,
diff --git a/index.js b/index.js
index 997466e..e08661a 100644
--- a/index.js
+++ b/index.js
@@ -1,30 +1,32 @@
-var types = require('./types')
-var rcodes = require('./rcodes')
-var opcodes = require('./opcodes')
-var ip = require('ip')
-var Buffer = require('safe-buffer').Buffer
+'use strict'
 
-var QUERY_FLAG = 0
-var RESPONSE_FLAG = 1 << 15
-var FLUSH_MASK = 1 << 15
-var NOT_FLUSH_MASK = ~FLUSH_MASK
-var QU_MASK = 1 << 15
-var NOT_QU_MASK = ~QU_MASK
+const types = require('./types')
+const rcodes = require('./rcodes')
+const opcodes = require('./opcodes')
+const ip = require('ip')
+const Buffer = require('safe-buffer').Buffer
 
-var name = exports.txt = exports.name = {}
+const QUERY_FLAG = 0
+const RESPONSE_FLAG = 1 << 15
+const FLUSH_MASK = 1 << 15
+const NOT_FLUSH_MASK = ~FLUSH_MASK
+const QU_MASK = 1 << 15
+const NOT_QU_MASK = ~QU_MASK
+
+const name = exports.txt = exports.name = {}
 
 name.encode = function (str, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(name.encodingLength(str))
   if (!offset) offset = 0
-  var oldOffset = offset
+  const oldOffset = offset
 
   // strip leading and trailing .
-  var n = str.replace(/^\.|\.$/gm, '')
+  const n = str.replace(/^\.|\.$/gm, '')
   if (n.length) {
-    var list = n.split('.')
+    const list = n.split('.')
 
-    for (var i = 0; i < list.length; i++) {
-      var len = buf.write(list[i], offset + 1)
+    for (let i = 0; i < list.length; i++) {
+      const len = buf.write(list[i], offset + 1)
       buf[offset] = len
       offset += len + 1
     }
@@ -41,16 +43,16 @@ name.encode.bytes = 0
 name.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var list = []
-  var oldOffset = offset
-  var len = buf[offset++]
+  const list = []
+  const oldOffset = offset
+  let len = buf[offset++]
 
   if (len === 0) {
     name.decode.bytes = 1
     return '.'
   }
   if (len >= 0xc0) {
-    var res = name.decode(buf, buf.readUInt16BE(offset - 1) - 0xc000)
+    const res = name.decode(buf, buf.readUInt16BE(offset - 1) - 0xc000)
     name.decode.bytes = 2
     return res
   }
@@ -77,13 +79,13 @@ name.encodingLength = function (n) {
   return Buffer.byteLength(n) + 2
 }
 
-var string = {}
+const string = {}
 
 string.encode = function (s, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(string.encodingLength(s))
   if (!offset) offset = 0
 
-  var len = buf.write(s, offset + 1)
+  const len = buf.write(s, offset + 1)
   buf[offset] = len
   string.encode.bytes = len + 1
   return buf
@@ -94,8 +96,8 @@ string.encode.bytes = 0
 string.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var len = buf[offset]
-  var s = buf.toString('utf-8', offset + 1, offset + 1 + len)
+  const len = buf[offset]
+  const s = buf.toString('utf-8', offset + 1, offset + 1 + len)
   string.decode.bytes = len + 1
   return s
 }
@@ -106,14 +108,14 @@ string.encodingLength = function (s) {
   return Buffer.byteLength(s) + 1
 }
 
-var header = {}
+const header = {}
 
 header.encode = function (h, buf, offset) {
   if (!buf) buf = header.encodingLength(h)
   if (!offset) offset = 0
 
-  var flags = (h.flags || 0) & 32767
-  var type = h.type === 'response' ? RESPONSE_FLAG : QUERY_FLAG
+  const flags = (h.flags || 0) & 32767
+  const type = h.type === 'response' ? RESPONSE_FLAG : QUERY_FLAG
 
   buf.writeUInt16BE(h.id || 0, offset)
   buf.writeUInt16BE(flags | type, offset + 2)
@@ -130,7 +132,7 @@ header.encode.bytes = 12
 header.decode = function (buf, offset) {
   if (!offset) offset = 0
   if (buf.length < 12) throw new Error('Header must be 12 bytes')
-  var flags = buf.readUInt16BE(offset + 2)
+  const flags = buf.readUInt16BE(offset + 2)
 
   return {
     id: buf.readUInt16BE(offset),
@@ -159,7 +161,7 @@ header.encodingLength = function () {
   return 12
 }
 
-var runknown = exports.unknown = {}
+const runknown = exports.unknown = {}
 
 runknown.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(runknown.encodingLength(data))
@@ -177,8 +179,8 @@ runknown.encode.bytes = 0
 runknown.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var len = buf.readUInt16BE(offset)
-  var data = buf.slice(offset + 2, offset + 2 + len)
+  const len = buf.readUInt16BE(offset)
+  const data = buf.slice(offset + 2, offset + 2 + len)
   runknown.decode.bytes = len + 2
   return data
 }
@@ -189,7 +191,7 @@ runknown.encodingLength = function (data) {
   return data.length + 2
 }
 
-var rns = exports.ns = {}
+const rns = exports.ns = {}
 
 rns.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rns.encodingLength(data))
@@ -206,8 +208,8 @@ rns.encode.bytes = 0
 rns.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var len = buf.readUInt16BE(offset)
-  var dd = name.decode(buf, offset + 2)
+  const len = buf.readUInt16BE(offset)
+  const dd = name.decode(buf, offset + 2)
 
   rns.decode.bytes = len + 2
   return dd
@@ -219,13 +221,13 @@ rns.encodingLength = function (data) {
   return name.encodingLength(data) + 2
 }
 
-var rsoa = exports.soa = {}
+const rsoa = exports.soa = {}
 
 rsoa.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rsoa.encodingLength(data))
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
   offset += 2
   name.encode(data.mname, buf, offset)
   offset += name.encode.bytes
@@ -252,9 +254,9 @@ rsoa.encode.bytes = 0
 rsoa.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
 
-  var data = {}
+  const data = {}
   offset += 2
   data.mname = name.decode(buf, offset)
   offset += name.decode.bytes
@@ -281,8 +283,8 @@ rsoa.encodingLength = function (data) {
   return 22 + name.encodingLength(data.mname) + name.encodingLength(data.rname)
 }
 
-var rtxt = exports.txt = exports.null = {}
-var rnull = rtxt
+const rtxt = exports.txt = exports.null = {}
+const rnull = rtxt
 
 rtxt.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rtxt.encodingLength(data))
@@ -291,10 +293,10 @@ rtxt.encode = function (data, buf, offset) {
   if (typeof data === 'string') data = Buffer.from(data)
   if (!data) data = Buffer.allocUnsafe(0)
 
-  var oldOffset = offset
+  const oldOffset = offset
   offset += 2
 
-  var len = data.length
+  const len = data.length
   data.copy(buf, offset, 0, len)
   offset += len
 
@@ -307,12 +309,12 @@ rtxt.encode.bytes = 0
 
 rtxt.decode = function (buf, offset) {
   if (!offset) offset = 0
-  var oldOffset = offset
-  var len = buf.readUInt16BE(offset)
+  const oldOffset = offset
+  const len = buf.readUInt16BE(offset)
 
   offset += 2
 
-  var data = buf.slice(offset, offset + len)
+  const data = buf.slice(offset, offset + len)
   offset += len
 
   rtxt.decode.bytes = offset - oldOffset
@@ -326,13 +328,13 @@ rtxt.encodingLength = function (data) {
   return (Buffer.isBuffer(data) ? data.length : Buffer.byteLength(data)) + 2
 }
 
-var rhinfo = exports.hinfo = {}
+const rhinfo = exports.hinfo = {}
 
 rhinfo.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rhinfo.encodingLength(data))
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
   offset += 2
   string.encode(data.cpu, buf, offset)
   offset += string.encode.bytes
@@ -348,9 +350,9 @@ rhinfo.encode.bytes = 0
 rhinfo.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
 
-  var data = {}
+  const data = {}
   offset += 2
   data.cpu = string.decode(buf, offset)
   offset += string.decode.bytes
@@ -366,9 +368,9 @@ rhinfo.encodingLength = function (data) {
   return string.encodingLength(data.cpu) + string.encodingLength(data.os) + 2
 }
 
-var rptr = exports.ptr = {}
-var rcname = exports.cname = rptr
-var rdname = exports.dname = rptr
+const rptr = exports.ptr = {}
+const rcname = exports.cname = rptr
+const rdname = exports.dname = rptr
 
 rptr.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rptr.encodingLength(data))
@@ -385,7 +387,7 @@ rptr.encode.bytes = 0
 rptr.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var data = name.decode(buf, offset + 2)
+  const data = name.decode(buf, offset + 2)
   rptr.decode.bytes = name.decode.bytes + 2
   return data
 }
@@ -396,7 +398,7 @@ rptr.encodingLength = function (data) {
   return name.encodingLength(data) + 2
 }
 
-var rsrv = exports.srv = {}
+const rsrv = exports.srv = {}
 
 rsrv.encode = function (data, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(rsrv.encodingLength(data))
@@ -407,7 +409,7 @@ rsrv.encode = function (data, buf, offset) {
   buf.writeUInt16BE(data.port || 0, offset + 6)
   name.encode(data.target, buf, offset + 8)
 
-  var len = name.encode.bytes + 6
+  const len = name.encode.bytes + 6
   buf.writeUInt16BE(len, offset)
 
   rsrv.encode.bytes = len + 2
@@ -419,9 +421,9 @@ rsrv.encode.bytes = 0
 rsrv.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var len = buf.readUInt16BE(offset)
+  const len = buf.readUInt16BE(offset)
 
-  var data = {}
+  const data = {}
   data.priority = buf.readUInt16BE(offset + 2)
   data.weight = buf.readUInt16BE(offset + 4)
   data.port = buf.readUInt16BE(offset + 6)
@@ -437,12 +439,12 @@ rsrv.encodingLength = function (data) {
   return 8 + name.encodingLength(data.target)
 }
 
-var rcaa = exports.caa = {}
+const rcaa = exports.caa = {}
 
 rcaa.ISSUER_CRITICAL = 1 << 7
 
 rcaa.encode = function (data, buf, offset) {
-  var len = rcaa.encodingLength(data)
+  const len = rcaa.encodingLength(data)
 
   if (!buf) buf = Buffer.allocUnsafe(rcaa.encodingLength(data))
   if (!offset) offset = 0
@@ -469,11 +471,11 @@ rcaa.encode.bytes = 0
 rcaa.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var len = buf.readUInt16BE(offset)
+  const len = buf.readUInt16BE(offset)
   offset += 2
 
-  var oldOffset = offset
-  var data = {}
+  const oldOffset = offset
+  const data = {}
   data.flags = buf.readUInt8(offset)
   offset += 1
   data.tag = string.decode(buf, offset)
@@ -493,7 +495,7 @@ rcaa.encodingLength = function (data) {
   return string.encodingLength(data.tag) + string.encodingLength(data.value) + 2
 }
 
-var ra = exports.a = {}
+const ra = exports.a = {}
 
 ra.encode = function (host, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(ra.encodingLength(host))
@@ -512,7 +514,7 @@ ra.decode = function (buf, offset) {
   if (!offset) offset = 0
 
   offset += 2
-  var host = ip.toString(buf, offset, 4)
+  const host = ip.toString(buf, offset, 4)
   ra.decode.bytes = 6
   return host
 }
@@ -523,7 +525,7 @@ ra.encodingLength = function () {
   return 6
 }
 
-var raaaa = exports.aaaa = {}
+const raaaa = exports.aaaa = {}
 
 raaaa.encode = function (host, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(raaaa.encodingLength(host))
@@ -542,7 +544,7 @@ raaaa.decode = function (buf, offset) {
   if (!offset) offset = 0
 
   offset += 2
-  var host = ip.toString(buf, offset, 16)
+  const host = ip.toString(buf, offset, 16)
   raaaa.decode.bytes = 18
   return host
 }
@@ -553,7 +555,7 @@ raaaa.encodingLength = function () {
   return 18
 }
 
-var renc = exports.record = function (type) {
+const renc = exports.record = function (type) {
   switch (type.toUpperCase()) {
     case 'A': return ra
     case 'PTR': return rptr
@@ -571,26 +573,26 @@ var renc = exports.record = function (type) {
   return runknown
 }
 
-var answer = exports.answer = {}
+const answer = exports.answer = {}
 
 answer.encode = function (a, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(answer.encodingLength(a))
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
 
   name.encode(a.name, buf, offset)
   offset += name.encode.bytes
 
   buf.writeUInt16BE(types.toType(a.type), offset)
 
-  var klass = a.class === undefined ? 1 : a.class
+  let klass = a.class === undefined ? 1 : a.class
   if (a.flush) klass |= FLUSH_MASK // the 1st bit of the class is the flush bit
   buf.writeUInt16BE(klass, offset + 2)
 
   buf.writeUInt32BE(a.ttl || 0, offset + 4)
 
-  var enc = renc(a.type)
+  const enc = renc(a.type)
   enc.encode(a.data, buf, offset + 8)
   offset += 8 + enc.encode.bytes
 
@@ -603,8 +605,8 @@ answer.encode.bytes = 0
 answer.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var a = {}
-  var oldOffset = offset
+  const a = {}
+  const oldOffset = offset
 
   a.name = name.decode(buf, offset)
   offset += name.decode.bytes
@@ -615,7 +617,7 @@ answer.decode = function (buf, offset) {
   a.flush = !!(a.class & FLUSH_MASK)
   if (a.flush) a.class &= NOT_FLUSH_MASK
 
-  var enc = renc(a.type)
+  const enc = renc(a.type)
   a.data = enc.decode(buf, offset + 8)
   offset += 8 + enc.decode.bytes
 
@@ -629,13 +631,13 @@ answer.encodingLength = function (a) {
   return name.encodingLength(a.name) + 8 + renc(a.type).encodingLength(a.data)
 }
 
-var question = exports.question = {}
+const question = exports.question = {}
 
 question.encode = function (q, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(question.encodingLength(q))
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
 
   name.encode(q.name, buf, offset)
   offset += name.encode.bytes
@@ -655,8 +657,8 @@ question.encode.bytes = 0
 question.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var oldOffset = offset
-  var q = {}
+  const oldOffset = offset
+  const q = {}
 
   q.name = name.decode(buf, offset)
   offset += name.decode.bytes
@@ -667,7 +669,7 @@ question.decode = function (buf, offset) {
   q.class = buf.readUInt16BE(offset)
   offset += 2
 
-  var qu = !!(q.class & QU_MASK)
+  const qu = !!(q.class & QU_MASK)
   if (qu) q.class &= NOT_QU_MASK
 
   question.decode.bytes = offset - oldOffset
@@ -691,7 +693,7 @@ exports.encode = function (result, buf, offset) {
   if (!buf) buf = Buffer.allocUnsafe(exports.encodingLength(result))
   if (!offset) offset = 0
 
-  var oldOffset = offset
+  const oldOffset = offset
 
   if (!result.questions) result.questions = []
   if (!result.answers) result.answers = []
@@ -716,8 +718,8 @@ exports.encode.bytes = 0
 exports.decode = function (buf, offset) {
   if (!offset) offset = 0
 
-  var oldOffset = offset
-  var result = header.decode(buf, offset)
+  const oldOffset = offset
+  const result = header.decode(buf, offset)
   offset += header.decode.bytes
 
   offset = decodeList(result.questions, question, buf, offset)
@@ -741,13 +743,13 @@ exports.encodingLength = function (result) {
 }
 
 function encodingLengthList (list, enc) {
-  var len = 0
-  for (var i = 0; i < list.length; i++) len += enc.encodingLength(list[i])
+  let len = 0
+  for (let i = 0; i < list.length; i++) len += enc.encodingLength(list[i])
   return len
 }
 
 function encodeList (list, enc, buf, offset) {
-  for (var i = 0; i < list.length; i++) {
+  for (let i = 0; i < list.length; i++) {
     enc.encode(list[i], buf, offset)
     offset += enc.encode.bytes
   }
@@ -755,7 +757,7 @@ function encodeList (list, enc, buf, offset) {
 }
 
 function decodeList (list, enc, buf, offset) {
-  for (var i = 0; i < list.length; i++) {
+  for (let i = 0; i < list.length; i++) {
     list[i] = enc.decode(buf, offset)
     offset += enc.decode.bytes
   }
diff --git a/opcodes.js b/opcodes.js
index 6b42db3..32b0a1b 100644
--- a/opcodes.js
+++ b/opcodes.js
@@ -1,3 +1,5 @@
+'use strict'
+
 /*
  * Traditional DNS header OPCODEs (4-bits) defined by IANA in
  * https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml#dns-parameters-5
diff --git a/package.json b/package.json
index b6f2c23..f2e3d53 100644
--- a/package.json
+++ b/package.json
@@ -2,27 +2,25 @@
   "name": "dns-packet",
   "version": "1.3.1",
   "description": "An abstract-encoding compliant module for encoding / decoding DNS packets",
-  "repository": {
-    "type": "git",
-    "url": "https://github.com/mafintosh/dns-packet"
-  },
-  "dependencies": {
-    "ip": "^1.1.0",
-    "safe-buffer": "^5.0.1"
-  },
-  "devDependencies": {
-    "eslint": "^4.15.0",
-    "standard": "^6.0.5",
-    "tape": "^4.4.0"
+  "author": "Mathias Buus",
+  "license": "MIT",
+  "repository": "mafintosh/dns-packet",
+  "homepage": "https://github.com/mafintosh/dns-packet",
+  "engines": {
+    "node": ">=4"
   },
   "scripts": {
     "test": "standard && eslint --color *.js && tape test.js"
   },
-  "bugs": {
-    "url": "https://github.com/mafintosh/dns-packet/issues"
+  "dependencies": {
+    "ip": "^1.1.5",
+    "safe-buffer": "^5.1.1"
+  },
+  "devDependencies": {
+    "eslint": "^4.15.0",
+    "standard": "^10.0.3",
+    "tape": "^4.8.0"
   },
-  "homepage": "https://github.com/mafintosh/dns-packet",
-  "main": "index.js",
   "keywords": [
     "dns",
     "packet",
@@ -36,7 +34,5 @@
     "types.js",
     "rcodes.js",
     "opcodes.js"
-  ],
-  "author": "Mathias Buus",
-  "license": "MIT"
+  ]
 }
diff --git a/rcodes.js b/rcodes.js
index 492b2f3..0500887 100644
--- a/rcodes.js
+++ b/rcodes.js
@@ -1,3 +1,5 @@
+'use strict'
+
 /*
  * Traditional DNS header RCODEs (4-bits) defined by IANA in
  * https://www.iana.org/assignments/dns-parameters/dns-parameters.xhtml
diff --git a/test.js b/test.js
index 0720cb3..2fa2ae9 100644
--- a/test.js
+++ b/test.js
@@ -1,8 +1,10 @@
-var tape = require('tape')
-var packet = require('./')
-var rcodes = require('./rcodes')
-var opcodes = require('./opcodes')
-var Buffer = require('safe-buffer').Buffer
+'use strict'
+
+const tape = require('tape')
+const packet = require('./')
+const rcodes = require('./rcodes')
+const opcodes = require('./opcodes')
+const Buffer = require('safe-buffer').Buffer
 
 tape('unknown', function (t) {
   testEncoder(t, packet.unknown, Buffer.from('hello world'))
@@ -176,19 +178,19 @@ tape('response', function (t) {
 })
 
 tape('rcode', function (t) {
-  var errors = ['NOERROR', 'FORMERR', 'SERVFAIL', 'NXDOMAIN', 'NOTIMP', 'REFUSED', 'YXDOMAIN', 'YXRRSET', 'NXRRSET', 'NOTAUTH', 'NOTZONE', 'RCODE_11', 'RCODE_12', 'RCODE_13', 'RCODE_14', 'RCODE_15']
-  for (var i in errors) {
-    var code = rcodes.toRcode(errors[i])
+  const errors = ['NOERROR', 'FORMERR', 'SERVFAIL', 'NXDOMAIN', 'NOTIMP', 'REFUSED', 'YXDOMAIN', 'YXRRSET', 'NXRRSET', 'NOTAUTH', 'NOTZONE', 'RCODE_11', 'RCODE_12', 'RCODE_13', 'RCODE_14', 'RCODE_15']
+  for (const i in errors) {
+    const code = rcodes.toRcode(errors[i])
     t.ok(errors[i] === rcodes.toString(code), 'rcode conversion from/to string matches: ' + rcodes.toString(code))
   }
 
-  var ops = ['QUERY', 'IQUERY', 'STATUS', 'OPCODE_3', 'NOTIFY', 'UPDATE', 'OPCODE_6', 'OPCODE_7', 'OPCODE_8', 'OPCODE_9', 'OPCODE_10', 'OPCODE_11', 'OPCODE_12', 'OPCODE_13', 'OPCODE_14', 'OPCODE_15']
-  for (var j in ops) {
-    var ocode = opcodes.toOpcode(ops[j])
+  const ops = ['QUERY', 'IQUERY', 'STATUS', 'OPCODE_3', 'NOTIFY', 'UPDATE', 'OPCODE_6', 'OPCODE_7', 'OPCODE_8', 'OPCODE_9', 'OPCODE_10', 'OPCODE_11', 'OPCODE_12', 'OPCODE_13', 'OPCODE_14', 'OPCODE_15']
+  for (const j in ops) {
+    const ocode = opcodes.toOpcode(ops[j])
     t.ok(ops[j] === opcodes.toString(ocode), 'opcode conversion from/to string matches: ' + opcodes.toString(ocode))
   }
 
-  var buf = packet.encode({
+  const buf = packet.encode({
     type: 'response',
     id: 45632,
     flags: 0x8480,
@@ -198,7 +200,7 @@ tape('rcode', function (t) {
       data: '127.0.0.1'
     }]
   })
-  var val = packet.decode(buf)
+  const val = packet.decode(buf)
   t.ok(val.type === 'response', 'decode type')
   t.ok(val.opcode === 'QUERY', 'decode opcode')
   t.ok(val.flag_qr === true, 'decode flag_auth')
@@ -214,12 +216,12 @@ tape('rcode', function (t) {
 })
 
 tape('name_encoding', function (t) {
-  var data = 'foo.example.com'
-  var buf = Buffer.allocUnsafe(255)
-  var offset = 0
+  let data = 'foo.example.com'
+  const buf = Buffer.allocUnsafe(255)
+  let offset = 0
   packet.name.encode(data, buf, offset)
   t.ok(packet.name.encode.bytes === 17, 'name encoding length matches')
-  var dd = packet.name.decode(buf, offset)
+  let dd = packet.name.decode(buf, offset)
   t.ok(data === dd, 'encode/decode matches')
   offset += packet.name.encode.bytes
 
@@ -246,15 +248,15 @@ tape('name_encoding', function (t) {
 })
 
 function testEncoder (t, rpacket, val) {
-  var buf = rpacket.encode(val)
-  var val2 = rpacket.decode(buf)
+  const buf = rpacket.encode(val)
+  const val2 = rpacket.decode(buf)
 
   t.same(buf.length, rpacket.encode.bytes, 'encode.bytes was set correctly')
   t.same(buf.length, rpacket.encodingLength(val), 'encoding length matches')
   t.ok(compare(t, val, val2), 'decoded object match')
 
-  var buf2 = rpacket.encode(val2)
-  var val3 = rpacket.decode(buf2)
+  const buf2 = rpacket.encode(val2)
+  const val3 = rpacket.decode(buf2)
 
   t.same(buf2.length, rpacket.encode.bytes, 'encode.bytes was set correctly on re-encode')
   t.same(buf2.length, rpacket.encodingLength(val), 'encoding length matches on re-encode')
@@ -262,10 +264,10 @@ function testEncoder (t, rpacket, val) {
   t.ok(compare(t, val, val3), 'decoded object match on re-encode')
   t.ok(compare(t, val2, val3), 're-encoded decoded object match on re-encode')
 
-  var bigger = Buffer.allocUnsafe(buf2.length + 10)
+  const bigger = Buffer.allocUnsafe(buf2.length + 10)
 
-  var buf3 = rpacket.encode(val, bigger, 10)
-  var val4 = rpacket.decode(buf3, 10)
+  const buf3 = rpacket.encode(val, bigger, 10)
+  const val4 = rpacket.decode(buf3, 10)
 
   t.ok(buf3 === bigger, 'echoes buffer on external buffer')
   t.same(rpacket.encode.bytes, buf.length, 'encode.bytes is the same on external buffer')
@@ -275,8 +277,8 @@ function testEncoder (t, rpacket, val) {
 function compare (t, a, b) {
   if (Buffer.isBuffer(a)) return a.toString('hex') === b.toString('hex')
   if (typeof a === 'object' && a && b) {
-    var keys = Object.keys(a)
-    for (var i = 0; i < keys.length; i++) {
+    const keys = Object.keys(a)
+    for (let i = 0; i < keys.length; i++) {
       if (!compare(t, a[keys[i]], b[keys[i]])) return false
     }
   } else {
diff --git a/types.js b/types.js
index 7a29d00..358eb49 100644
--- a/types.js
+++ b/types.js
@@ -1,3 +1,5 @@
+'use strict'
+
 exports.toString = function (type) {
   switch (type) {
     case 1: return 'A'