From 1035f3c1d8dadc12b1b1d3ebfb6ab8fdcbc4c49e Mon Sep 17 00:00:00 2001
From: Vincent Weevers <mail@vincentweevers.nl>
Date: Fri, 9 Apr 2021 21:11:19 +0200
Subject: [PATCH] Modernize syntax and bump standard (Level/community#98)

---
 .github/dependabot.yml |  2 -
 index.js               | 89 +++++++++++++++++++++++-------------------
 iterator.js            | 43 ++++++++++----------
 package.json           |  2 +-
 test/custom-test.js    | 66 +++++++++++++++----------------
 test/index.js          | 10 ++---
 test/support-test.js   |  6 +--
 test/upgrade-test.js   | 10 ++---
 util/clear.js          | 12 +++---
 util/deserialize.js    | 12 +++---
 util/key-range.js      | 12 +++---
 util/serialize.js      |  6 +--
 util/support.js        |  2 +-
 13 files changed, 139 insertions(+), 133 deletions(-)

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index 5d7f065..a571853 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -5,7 +5,5 @@ updates:
     schedule:
       interval: monthly
     ignore:
-      - dependency-name: buffer
       - dependency-name: dependency-check
       - dependency-name: uuid
-      - dependency-name: standard
diff --git a/index.js b/index.js
index 397cb5f..1d244bd 100644
--- a/index.js
+++ b/index.js
@@ -4,16 +4,16 @@
 
 module.exports = Level
 
-var AbstractLevelDOWN = require('abstract-leveldown').AbstractLevelDOWN
-var inherits = require('inherits')
-var Iterator = require('./iterator')
-var serialize = require('./util/serialize')
-var deserialize = require('./util/deserialize')
-var support = require('./util/support')
-var clear = require('./util/clear')
-var createKeyRange = require('./util/key-range')
+const AbstractLevelDOWN = require('abstract-leveldown').AbstractLevelDOWN
+const inherits = require('inherits')
+const Iterator = require('./iterator')
+const serialize = require('./util/serialize')
+const deserialize = require('./util/deserialize')
+const support = require('./util/support')
+const clear = require('./util/clear')
+const createKeyRange = require('./util/key-range')
 
-var DEFAULT_PREFIX = 'level-js-'
+const DEFAULT_PREFIX = 'level-js-'
 
 function Level (location, opts) {
   if (!(this instanceof Level)) return new Level(location, opts)
@@ -41,34 +41,33 @@ inherits(Level, AbstractLevelDOWN)
 Level.prototype.type = 'level-js'
 
 Level.prototype._open = function (options, callback) {
-  var req = indexedDB.open(this.prefix + this.location, this.version)
-  var self = this
+  const req = indexedDB.open(this.prefix + this.location, this.version)
 
   req.onerror = function () {
     callback(req.error || new Error('unknown error'))
   }
 
-  req.onsuccess = function () {
-    self.db = req.result
+  req.onsuccess = () => {
+    this.db = req.result
     callback()
   }
 
-  req.onupgradeneeded = function (ev) {
-    var db = ev.target.result
+  req.onupgradeneeded = (ev) => {
+    const db = ev.target.result
 
-    if (!db.objectStoreNames.contains(self.location)) {
-      db.createObjectStore(self.location)
+    if (!db.objectStoreNames.contains(this.location)) {
+      db.createObjectStore(this.location)
     }
   }
 }
 
 Level.prototype.store = function (mode) {
-  var transaction = this.db.transaction([this.location], mode)
+  const transaction = this.db.transaction([this.location], mode)
   return transaction.objectStore(this.location)
 }
 
 Level.prototype.await = function (request, callback) {
-  var transaction = request.transaction
+  const transaction = request.transaction
 
   // Take advantage of the fact that a non-canceled request error aborts
   // the transaction. I.e. no need to listen for "request.onerror".
@@ -82,10 +81,11 @@ Level.prototype.await = function (request, callback) {
 }
 
 Level.prototype._get = function (key, options, callback) {
-  var store = this.store('readonly')
+  const store = this.store('readonly')
+  let req
 
   try {
-    var req = store.get(key)
+    req = store.get(key)
   } catch (err) {
     return this._nextTick(callback, err)
   }
@@ -103,10 +103,11 @@ Level.prototype._get = function (key, options, callback) {
 }
 
 Level.prototype._del = function (key, options, callback) {
-  var store = this.store('readwrite')
+  const store = this.store('readwrite')
+  let req
 
   try {
-    var req = store.delete(key)
+    req = store.delete(key)
   } catch (err) {
     return this._nextTick(callback, err)
   }
@@ -115,12 +116,13 @@ Level.prototype._del = function (key, options, callback) {
 }
 
 Level.prototype._put = function (key, value, options, callback) {
-  var store = this.store('readwrite')
+  const store = this.store('readwrite')
+  let req
 
   try {
     // Will throw a DataError or DataCloneError if the environment
     // does not support serializing the key or value respectively.
-    var req = store.put(value, key)
+    req = store.put(value, key)
   } catch (err) {
     return this._nextTick(callback, err)
   }
@@ -143,10 +145,10 @@ Level.prototype._iterator = function (options) {
 Level.prototype._batch = function (operations, options, callback) {
   if (operations.length === 0) return this._nextTick(callback)
 
-  var store = this.store('readwrite')
-  var transaction = store.transaction
-  var index = 0
-  var error
+  const store = this.store('readwrite')
+  const transaction = store.transaction
+  let index = 0
+  let error
 
   transaction.onabort = function () {
     callback(error || transaction.error || new Error('aborted by user'))
@@ -158,11 +160,13 @@ Level.prototype._batch = function (operations, options, callback) {
 
   // Wait for a request to complete before making the next, saving CPU.
   function loop () {
-    var op = operations[index++]
-    var key = op.key
+    const op = operations[index++]
+    const key = op.key
+
+    let req
 
     try {
-      var req = op.type === 'del' ? store.delete(key) : store.put(op.value, key)
+      req = op.type === 'del' ? store.delete(key) : store.put(op.value, key)
     } catch (err) {
       error = err
       transaction.abort()
@@ -178,8 +182,11 @@ Level.prototype._batch = function (operations, options, callback) {
 }
 
 Level.prototype._clear = function (options, callback) {
+  let keyRange
+  let req
+
   try {
-    var keyRange = createKeyRange(options)
+    keyRange = createKeyRange(options)
   } catch (e) {
     // The lower key is greater than the upper key.
     // IndexedDB throws an error, but we'll just do nothing.
@@ -193,8 +200,8 @@ Level.prototype._clear = function (options, callback) {
   }
 
   try {
-    var store = this.store('readwrite')
-    var req = keyRange ? store.delete(keyRange) : store.clear()
+    const store = this.store('readwrite')
+    req = keyRange ? store.delete(keyRange) : store.clear()
   } catch (err) {
     return this._nextTick(callback, err)
   }
@@ -213,9 +220,9 @@ Level.prototype.upgrade = function (callback) {
     return this._nextTick(callback, new Error('cannot upgrade() before open()'))
   }
 
-  var it = this.iterator()
-  var batchOptions = {}
-  var self = this
+  const it = this.iterator()
+  const batchOptions = {}
+  const self = this
 
   it._deserializeKey = it._deserializeValue = identity
   next()
@@ -230,8 +237,8 @@ Level.prototype.upgrade = function (callback) {
       return finish(err)
     }
 
-    var newKey = self._serializeKey(deserialize(key, true))
-    var newValue = self._serializeValue(deserialize(value, true))
+    const newKey = self._serializeKey(deserialize(key, true))
+    const newValue = self._serializeValue(deserialize(value, true))
 
     // To bypass serialization on the old key, use _batch() instead of batch().
     // NOTE: if we disable snapshotting (#86) this could lead to a loop of
@@ -259,7 +266,7 @@ Level.destroy = function (location, prefix, callback) {
     callback = prefix
     prefix = DEFAULT_PREFIX
   }
-  var request = indexedDB.deleteDatabase(prefix + location)
+  const request = indexedDB.deleteDatabase(prefix + location)
   request.onsuccess = function () {
     callback()
   }
diff --git a/iterator.js b/iterator.js
index ec5bddb..0a10f0a 100644
--- a/iterator.js
+++ b/iterator.js
@@ -1,10 +1,10 @@
 'use strict'
 
-var inherits = require('inherits')
-var AbstractIterator = require('abstract-leveldown').AbstractIterator
-var createKeyRange = require('./util/key-range')
-var deserialize = require('./util/deserialize')
-var noop = function () {}
+const inherits = require('inherits')
+const AbstractIterator = require('abstract-leveldown').AbstractIterator
+const createKeyRange = require('./util/key-range')
+const deserialize = require('./util/deserialize')
+const noop = function () {}
 
 module.exports = Iterator
 
@@ -30,8 +30,10 @@ function Iterator (db, location, options) {
     return
   }
 
+  let keyRange
+
   try {
-    var keyRange = createKeyRange(options)
+    keyRange = createKeyRange(options)
   } catch (e) {
     // The lower key is greater than the upper key.
     // IndexedDB throws an error, but we'll just return 0 results.
@@ -45,25 +47,24 @@ function Iterator (db, location, options) {
 inherits(Iterator, AbstractIterator)
 
 Iterator.prototype.createIterator = function (location, keyRange, reverse) {
-  var self = this
-  var transaction = this.db.db.transaction([location], 'readonly')
-  var store = transaction.objectStore(location)
-  var req = store.openCursor(keyRange, reverse ? 'prev' : 'next')
-
-  req.onsuccess = function (ev) {
-    var cursor = ev.target.result
-    if (cursor) self.onItem(cursor)
+  const transaction = this.db.db.transaction([location], 'readonly')
+  const store = transaction.objectStore(location)
+  const req = store.openCursor(keyRange, reverse ? 'prev' : 'next')
+
+  req.onsuccess = (ev) => {
+    const cursor = ev.target.result
+    if (cursor) this.onItem(cursor)
   }
 
   this._transaction = transaction
 
   // If an error occurs (on the request), the transaction will abort.
-  transaction.onabort = function () {
-    self.onAbort(self._transaction.error || new Error('aborted by user'))
+  transaction.onabort = () => {
+    this.onAbort(this._transaction.error || new Error('aborted by user'))
   }
 
-  transaction.oncomplete = function () {
-    self.onComplete()
+  transaction.oncomplete = () => {
+    this.onComplete()
   }
 }
 
@@ -98,12 +99,12 @@ Iterator.prototype.maybeNext = function () {
 Iterator.prototype._next = function (callback) {
   if (this._aborted) {
     // The error should be picked up by either next() or end().
-    var err = this._error
+    const err = this._error
     this._error = null
     this._nextTick(callback, err)
   } else if (this._cache.length > 0) {
-    var key = this._cache.shift()
-    var value = this._cache.shift()
+    let key = this._cache.shift()
+    let value = this._cache.shift()
 
     if (this._keys && key !== undefined) {
       key = this._deserializeKey(key, this._keyAsBuffer)
diff --git a/package.json b/package.json
index 6b88cd2..5daf701 100644
--- a/package.json
+++ b/package.json
@@ -38,7 +38,7 @@
     "level-community": "^3.0.0",
     "level-concat-iterator": "^2.0.0",
     "nyc": "^15.0.0",
-    "standard": "^15.0.1",
+    "standard": "^16.0.3",
     "tape": "^5.0.0",
     "uuid": "^3.3.2"
   },
diff --git a/test/custom-test.js b/test/custom-test.js
index 5d63140..64d29a3 100644
--- a/test/custom-test.js
+++ b/test/custom-test.js
@@ -1,12 +1,12 @@
 'use strict'
 
-var concat = require('level-concat-iterator')
+const concat = require('level-concat-iterator')
 
 module.exports = function (leveljs, test, testCommon) {
   test('setUp', testCommon.setUp)
 
   test('default prefix', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     t.ok(db.location, 'instance has location property')
     t.is(db.prefix, 'level-js-', 'instance has prefix property')
@@ -14,9 +14,9 @@ module.exports = function (leveljs, test, testCommon) {
     db.open(function (err) {
       t.notOk(err, 'no open error')
 
-      var idb = db.db
-      var databaseName = idb.name
-      var storeNames = idb.objectStoreNames
+      const idb = db.db
+      const databaseName = idb.name
+      const storeNames = idb.objectStoreNames
 
       t.is(databaseName, 'level-js-' + db.location, 'database name is prefixed')
       t.is(storeNames.length, 1, 'created 1 object store')
@@ -27,7 +27,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('custom prefix', function (t) {
-    var db = testCommon.factory({ prefix: 'custom-' })
+    const db = testCommon.factory({ prefix: 'custom-' })
 
     t.ok(db.location, 'instance has location property')
     t.is(db.prefix, 'custom-', 'instance has prefix property')
@@ -35,9 +35,9 @@ module.exports = function (leveljs, test, testCommon) {
     db.open(function (err) {
       t.notOk(err, 'no open error')
 
-      var idb = db.db
-      var databaseName = idb.name
-      var storeNames = idb.objectStoreNames
+      const idb = db.db
+      const databaseName = idb.name
+      const storeNames = idb.objectStoreNames
 
       t.is(databaseName, 'custom-' + db.location, 'database name is prefixed')
       t.is(storeNames.length, 1, 'created 1 object store')
@@ -48,7 +48,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('empty prefix', function (t) {
-    var db = testCommon.factory({ prefix: '' })
+    const db = testCommon.factory({ prefix: '' })
 
     t.ok(db.location, 'instance has location property')
     t.is(db.prefix, '', 'instance has prefix property')
@@ -56,9 +56,9 @@ module.exports = function (leveljs, test, testCommon) {
     db.open(function (err) {
       t.notOk(err, 'no open error')
 
-      var idb = db.db
-      var databaseName = idb.name
-      var storeNames = idb.objectStoreNames
+      const idb = db.db
+      const databaseName = idb.name
+      const storeNames = idb.objectStoreNames
 
       t.is(databaseName, db.location, 'database name is prefixed')
       t.is(storeNames.length, 1, 'created 1 object store')
@@ -69,7 +69,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('put Buffer value, get Buffer value', function (t) {
-    var level = testCommon.factory()
+    const level = testCommon.factory()
     level.open(function (err) {
       t.notOk(err, 'no error')
       level.put('key', Buffer.from('00ff', 'hex'), function (err) {
@@ -85,7 +85,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('put Buffer value, get string value', function (t) {
-    var level = testCommon.factory()
+    const level = testCommon.factory()
     level.open(function (err) {
       t.notOk(err, 'no error')
       level.put('key', Buffer.from('abc'), function (err) {
@@ -100,7 +100,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('put utf8 string, get utf8 string', function (t) {
-    var level = testCommon.factory()
+    const level = testCommon.factory()
     level.open(function (err) {
       t.notOk(err, 'no error')
       level.put('💩', '💩', function (err) {
@@ -118,7 +118,7 @@ module.exports = function (leveljs, test, testCommon) {
   // prevented by process.browser checks (Level/abstract-leveldown#121).
   // This test is adapted from memdown.
   test('buffer keys', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     if (!db.supports.bufferKeys) {
       t.fail('environment does not support buffer keys')
@@ -128,8 +128,8 @@ module.exports = function (leveljs, test, testCommon) {
     db.open(function (err) {
       t.ifError(err, 'no open error')
 
-      var one = Buffer.from('80', 'hex')
-      var two = Buffer.from('c0', 'hex')
+      const one = Buffer.from('80', 'hex')
+      const two = Buffer.from('c0', 'hex')
 
       t.ok(two.toString() === one.toString(), 'would be equal when not buffer-aware')
       t.ok(Buffer.compare(two, one) > 0, 'but greater when buffer-aware')
@@ -162,7 +162,7 @@ module.exports = function (leveljs, test, testCommon) {
   // This should be covered by abstract-leveldown tests, but that's
   // prevented by process.browser checks (Level/abstract-leveldown#121).
   test('iterator yields buffer keys', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     if (!db.supports.bufferKeys) {
       t.fail('environment does not support buffer keys')
@@ -178,7 +178,7 @@ module.exports = function (leveljs, test, testCommon) {
       ], function (err) {
         t.ifError(err, 'no batch error')
 
-        var it = db.iterator({ valueAsBuffer: false })
+        const it = db.iterator({ valueAsBuffer: false })
         concat(it, function (err, entries) {
           t.ifError(err, 'no iterator error')
 
@@ -197,7 +197,7 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('buffer range option', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     if (!db.supports.bufferKeys) {
       t.fail('environment does not support buffer keys')
@@ -207,8 +207,8 @@ module.exports = function (leveljs, test, testCommon) {
     db.open(function (err) {
       t.ifError(err, 'no open error')
 
-      var one = Buffer.from('80', 'hex')
-      var two = Buffer.from('c0', 'hex')
+      const one = Buffer.from('80', 'hex')
+      const two = Buffer.from('c0', 'hex')
 
       db.batch([
         { type: 'put', key: one, value: one },
@@ -233,7 +233,7 @@ module.exports = function (leveljs, test, testCommon) {
   test('iterator stringifies buffer input', function (t) {
     t.plan(6)
 
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     db.open(function (err) {
       t.ifError(err, 'no open error')
@@ -258,8 +258,8 @@ module.exports = function (leveljs, test, testCommon) {
   // then create it again, then try and destroy it again. these avoid doing that
 
   test('test .destroy', function (t) {
-    var db = testCommon.factory()
-    var location = db.location
+    const db = testCommon.factory()
+    const location = db.location
     db.open(function (err) {
       t.notOk(err, 'no error')
       db.put('key', 'value', function (err) {
@@ -271,7 +271,7 @@ module.exports = function (leveljs, test, testCommon) {
             t.notOk(err, 'no error')
             leveljs.destroy(location, function (err) {
               t.notOk(err, 'no error')
-              var db2 = leveljs(location)
+              const db2 = leveljs(location)
               db2.open(function (err) {
                 t.notOk(err, 'no error')
                 db2.get('key', { asBuffer: false }, function (err, value) {
@@ -287,9 +287,9 @@ module.exports = function (leveljs, test, testCommon) {
   })
 
   test('test .destroy and custom prefix', function (t) {
-    var prefix = 'custom-'
-    var db = testCommon.factory({ prefix: prefix })
-    var location = db.location
+    const prefix = 'custom-'
+    const db = testCommon.factory({ prefix: prefix })
+    const location = db.location
 
     db.open(function (err) {
       t.notOk(err, 'no error')
@@ -302,7 +302,7 @@ module.exports = function (leveljs, test, testCommon) {
             t.notOk(err, 'no error')
             leveljs.destroy(location, prefix, function (err) {
               t.notOk(err, 'no error')
-              var db2 = leveljs(location, { prefix: prefix })
+              const db2 = leveljs(location, { prefix: prefix })
               db2.open(function (err) {
                 t.notOk(err, 'no error')
                 db2.get('key', { asBuffer: false }, function (err, value) {
@@ -319,7 +319,7 @@ module.exports = function (leveljs, test, testCommon) {
 
   // TODO: move to abstract-leveldown test suite (and add to iterator tests too)
   test('clear() with lower key greater than upper key', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
     db.open(function (err) {
       t.ifError(err, 'no open error')
diff --git a/test/index.js b/test/index.js
index 7feb50e..230e25d 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,14 +1,14 @@
 'use strict'
 
-var test = require('tape')
-var uuid = require('uuid/v4')
-var suite = require('abstract-leveldown/test')
-var leveljs = require('..')
+const test = require('tape')
+const uuid = require('uuid/v4')
+const suite = require('abstract-leveldown/test')
+const leveljs = require('..')
 
 // Test feature detection
 require('./support-test')(leveljs, test)
 
-var testCommon = suite.common({
+const testCommon = suite.common({
   test: test,
   factory: function (opts) {
     return leveljs(uuid(), opts)
diff --git a/test/support-test.js b/test/support-test.js
index df514bb..2b37caf 100644
--- a/test/support-test.js
+++ b/test/support-test.js
@@ -1,9 +1,9 @@
 'use strict'
 
-var support = require('../util/support')
+const support = require('../util/support')
 
-var pos = function () { }
-var neg = function () { throw new Error() }
+const pos = function () { }
+const neg = function () { throw new Error() }
 
 module.exports = function (leveljs, test) {
   test('mock bufferKeys support', function (t) {
diff --git a/test/upgrade-test.js b/test/upgrade-test.js
index 8a15887..5049b47 100644
--- a/test/upgrade-test.js
+++ b/test/upgrade-test.js
@@ -1,19 +1,19 @@
 'use strict'
 
-var concat = require('level-concat-iterator')
+const concat = require('level-concat-iterator')
 
 module.exports = function (leveljs, test, testCommon) {
   test('upgrade', function (t) {
-    var db = testCommon.factory()
+    const db = testCommon.factory()
 
-    var input = [
+    const input = [
       { key: -1, value: 'a' },
       { key: '0', value: ab('b') },
       { key: '1', value: 1 },
       { key: ab('2'), value: new Uint8Array(ab('2')) }
     ]
 
-    var output = [
+    const output = [
       { key: ab('-1'), value: new Uint8Array(ab('a')) },
       { key: ab('0'), value: new Uint8Array(ab('b')) },
       { key: ab('1'), value: new Uint8Array(ab('1')) },
@@ -46,7 +46,7 @@ module.exports = function (leveljs, test, testCommon) {
     })
 
     function concatRaw (callback) {
-      var it = db.iterator()
+      const it = db.iterator()
       it._deserializeKey = it._deserializeValue = identity
       concat(it, callback)
     }
diff --git a/util/clear.js b/util/clear.js
index 3837d86..5efcf6f 100644
--- a/util/clear.js
+++ b/util/clear.js
@@ -3,9 +3,9 @@
 module.exports = function clear (db, location, keyRange, options, callback) {
   if (options.limit === 0) return db._nextTick(callback)
 
-  var transaction = db.db.transaction([location], 'readwrite')
-  var store = transaction.objectStore(location)
-  var count = 0
+  const transaction = db.db.transaction([location], 'readwrite')
+  const store = transaction.objectStore(location)
+  let count = 0
 
   transaction.oncomplete = function () {
     callback()
@@ -16,11 +16,11 @@ module.exports = function clear (db, location, keyRange, options, callback) {
   }
 
   // A key cursor is faster (skips reading values) but not supported by IE
-  var method = store.openKeyCursor ? 'openKeyCursor' : 'openCursor'
-  var direction = options.reverse ? 'prev' : 'next'
+  const method = store.openKeyCursor ? 'openKeyCursor' : 'openCursor'
+  const direction = options.reverse ? 'prev' : 'next'
 
   store[method](keyRange, direction).onsuccess = function (ev) {
-    var cursor = ev.target.result
+    const cursor = ev.target.result
 
     if (cursor) {
       // Wait for a request to complete before continuing, saving CPU.
diff --git a/util/deserialize.js b/util/deserialize.js
index f54c8f6..a79868a 100644
--- a/util/deserialize.js
+++ b/util/deserialize.js
@@ -1,9 +1,9 @@
 'use strict'
 
-var Buffer = require('buffer').Buffer
-var ta2str = (function () {
+const Buffer = require('buffer').Buffer
+const ta2str = (function () {
   if (global.TextDecoder) {
-    var decoder = new TextDecoder('utf-8')
+    const decoder = new TextDecoder('utf-8')
     return decoder.decode.bind(decoder)
   } else {
     return function ta2str (ta) {
@@ -12,9 +12,9 @@ var ta2str = (function () {
   }
 })()
 
-var ab2str = (function () {
+const ab2str = (function () {
   if (global.TextDecoder) {
-    var decoder = new TextDecoder('utf-8')
+    const decoder = new TextDecoder('utf-8')
     return decoder.decode.bind(decoder)
   } else {
     return function ab2str (ab) {
@@ -24,7 +24,7 @@ var ab2str = (function () {
 })()
 
 function ta2buf (ta) {
-  var buf = Buffer.from(ta.buffer)
+  const buf = Buffer.from(ta.buffer)
 
   if (ta.byteLength === ta.buffer.byteLength) {
     return buf
diff --git a/util/key-range.js b/util/key-range.js
index 74fac14..7526958 100644
--- a/util/key-range.js
+++ b/util/key-range.js
@@ -2,14 +2,14 @@
 
 'use strict'
 
-var ltgt = require('ltgt')
-var NONE = {}
+const ltgt = require('ltgt')
+const NONE = Symbol('none')
 
 module.exports = function createKeyRange (options) {
-  var lower = ltgt.lowerBound(options, NONE)
-  var upper = ltgt.upperBound(options, NONE)
-  var lowerOpen = ltgt.lowerBoundExclusive(options, NONE)
-  var upperOpen = ltgt.upperBoundExclusive(options, NONE)
+  const lower = ltgt.lowerBound(options, NONE)
+  const upper = ltgt.upperBound(options, NONE)
+  const lowerOpen = ltgt.lowerBoundExclusive(options, NONE)
+  const upperOpen = ltgt.upperBoundExclusive(options, NONE)
 
   if (lower !== NONE && upper !== NONE) {
     return IDBKeyRange.bound(lower, upper, lowerOpen, upperOpen)
diff --git a/util/serialize.js b/util/serialize.js
index 8fa0f0a..e2f7d1d 100644
--- a/util/serialize.js
+++ b/util/serialize.js
@@ -1,11 +1,11 @@
 'use strict'
 
-var Buffer = require('buffer').Buffer
+const Buffer = require('buffer').Buffer
 // Returns either a Uint8Array or Buffer (doesn't matter to
 // IndexedDB, because Buffer is a subclass of Uint8Array)
-var str2bin = (function () {
+const str2bin = (function () {
   if (global.TextEncoder) {
-    var encoder = new TextEncoder('utf-8')
+    const encoder = new TextEncoder('utf-8')
     return encoder.encode.bind(encoder)
   } else {
     return Buffer.from
diff --git a/util/support.js b/util/support.js
index 7b90211..d864e1b 100644
--- a/util/support.js
+++ b/util/support.js
@@ -1,6 +1,6 @@
 'use strict'
 
-var Buffer = require('buffer').Buffer
+const Buffer = require('buffer').Buffer
 
 exports.test = function (key) {
   return function test (impl) {