diff --git a/lib/directive-container.js b/lib/directive-container.js
index d27333a..d4d889c 100644
--- a/lib/directive-container.js
+++ b/lib/directive-container.js
@@ -10,18 +10,18 @@ export const directiveContainer = {
   concrete: true
 }
 
-var label = {tokenize: tokenizeLabel, partial: true}
-var attributes = {tokenize: tokenizeAttributes, partial: true}
+const label = {tokenize: tokenizeLabel, partial: true}
+const attributes = {tokenize: tokenizeAttributes, partial: true}
 
 function tokenizeDirectiveContainer(effects, ok, nok) {
-  var self = this
+  const self = this
   const tail = self.events[self.events.length - 1]
   const initialSize =
     tail && tail[1].type === 'linePrefix'
       ? tail[2].sliceSerialize(tail[1], true).length
       : 0
-  var sizeOpen = 0
-  var previous
+  let sizeOpen = 0
+  let previous
 
   return start
 
@@ -114,13 +114,14 @@ function tokenizeDirectiveContainer(effects, ok, nok) {
   }
 
   function chunkStart(code) {
-    var token
-
     if (code === null) {
       return after(code)
     }
 
-    token = effects.enter('chunkDocument', {contentType: 'document', previous})
+    const token = effects.enter('chunkDocument', {
+      contentType: 'document',
+      previous
+    })
     if (previous) previous.next = token
     previous = token
     return contentContinue(code)
@@ -149,7 +150,7 @@ function tokenizeDirectiveContainer(effects, ok, nok) {
   }
 
   function tokenizeClosingFence(effects, ok, nok) {
-    var size = 0
+    let size = 0
 
     return factorySpace(effects, closingPrefixAfter, 'linePrefix', 4)
 
diff --git a/lib/directive-leaf.js b/lib/directive-leaf.js
index 5c5016c..1cbb706 100644
--- a/lib/directive-leaf.js
+++ b/lib/directive-leaf.js
@@ -8,11 +8,11 @@ export const directiveLeaf = {
   tokenize: tokenizeDirectiveLeaf
 }
 
-var label = {tokenize: tokenizeLabel, partial: true}
-var attributes = {tokenize: tokenizeAttributes, partial: true}
+const label = {tokenize: tokenizeLabel, partial: true}
+const attributes = {tokenize: tokenizeAttributes, partial: true}
 
 function tokenizeDirectiveLeaf(effects, ok, nok) {
-  var self = this
+  const self = this
 
   return start
 
diff --git a/lib/directive-text.js b/lib/directive-text.js
index 91ba096..d50ab94 100644
--- a/lib/directive-text.js
+++ b/lib/directive-text.js
@@ -7,8 +7,8 @@ export const directiveText = {
   previous
 }
 
-var label = {tokenize: tokenizeLabel, partial: true}
-var attributes = {tokenize: tokenizeAttributes, partial: true}
+const label = {tokenize: tokenizeLabel, partial: true}
+const attributes = {tokenize: tokenizeAttributes, partial: true}
 
 function previous(code) {
   // If there is a previous code, there will always be a tail.
@@ -19,7 +19,7 @@ function previous(code) {
 }
 
 function tokenizeDirectiveText(effects, ok, nok) {
-  var self = this
+  const self = this
 
   return start
 
diff --git a/lib/factory-attributes.js b/lib/factory-attributes.js
index 61d1e0c..f674e9e 100644
--- a/lib/factory-attributes.js
+++ b/lib/factory-attributes.js
@@ -26,8 +26,8 @@ export function factoryAttributes(
   attributeValueData,
   disallowEol
 ) {
-  var type
-  var marker
+  let type
+  let marker
 
   return start
 
diff --git a/lib/factory-label.js b/lib/factory-label.js
index 4857c26..015763a 100644
--- a/lib/factory-label.js
+++ b/lib/factory-label.js
@@ -15,8 +15,8 @@ export function factoryLabel(
   stringType,
   disallowEol
 ) {
-  var size = 0
-  var balance = 0
+  let size = 0
+  let balance = 0
 
   return start
 
diff --git a/lib/factory-name.js b/lib/factory-name.js
index 3fcfb31..07a83d8 100644
--- a/lib/factory-name.js
+++ b/lib/factory-name.js
@@ -1,7 +1,7 @@
 import {asciiAlpha, asciiAlphanumeric} from 'micromark-util-character'
 
 export function factoryName(effects, ok, nok, nameType) {
-  var self = this
+  const self = this
 
   return start
 
diff --git a/lib/html.js b/lib/html.js
index 5f3a9a5..d598ad8 100644
--- a/lib/html.js
+++ b/lib/html.js
@@ -1,9 +1,9 @@
 import {decodeEntity} from 'parse-entities/decode-entity.js'
 
-var own = {}.hasOwnProperty
+const own = {}.hasOwnProperty
 
 export function directiveHtml(options) {
-  var extensions = options || {}
+  const extensions = options || {}
 
   return {
     enter: {
@@ -65,13 +65,13 @@ export function directiveHtml(options) {
   }
 
   function enter(type) {
-    var stack = this.getData('directiveStack')
+    let stack = this.getData('directiveStack')
     if (!stack) this.setData('directiveStack', (stack = []))
     stack.push({type})
   }
 
   function exitName(token) {
-    var stack = this.getData('directiveStack')
+    const stack = this.getData('directiveStack')
     stack[stack.length - 1].name = this.sliceSerialize(token)
   }
 
@@ -80,8 +80,8 @@ export function directiveHtml(options) {
   }
 
   function exitLabel() {
-    var data = this.resume()
-    var stack = this.getData('directiveStack')
+    const data = this.resume()
+    const stack = this.getData('directiveStack')
     stack[stack.length - 1].label = data
   }
 
@@ -111,18 +111,18 @@ export function directiveHtml(options) {
   }
 
   function exitAttributeValue(token) {
-    var attributes = this.getData('directiveAttributes')
+    const attributes = this.getData('directiveAttributes')
     attributes[attributes.length - 1][1] = decodeLight(
       this.sliceSerialize(token)
     )
   }
 
   function exitAttributes() {
-    var stack = this.getData('directiveStack')
-    var attributes = this.getData('directiveAttributes')
-    var cleaned = {}
-    var index = -1
-    var attribute
+    const stack = this.getData('directiveStack')
+    const attributes = this.getData('directiveAttributes')
+    const cleaned = {}
+    let index = -1
+    let attribute
 
     while (++index < attributes.length) {
       attribute = attributes[index]
@@ -144,23 +144,23 @@ export function directiveHtml(options) {
   }
 
   function exitContainerContent() {
-    var data = this.resume()
-    var stack = this.getData('directiveStack')
+    const data = this.resume()
+    const stack = this.getData('directiveStack')
     stack[stack.length - 1].content = data
   }
 
   function exitContainerFence() {
-    var stack = this.getData('directiveStack')
-    var directive = stack[stack.length - 1]
+    const stack = this.getData('directiveStack')
+    const directive = stack[stack.length - 1]
     if (!directive.fenceCount) directive.fenceCount = 0
     directive.fenceCount++
     if (directive.fenceCount === 1) this.setData('slurpOneLineEnding', true)
   }
 
   function exit() {
-    var directive = this.getData('directiveStack').pop()
-    var found
-    var result
+    const directive = this.getData('directiveStack').pop()
+    let found
+    let result
 
     if (own.call(extensions, directive.name)) {
       result = extensions[directive.name].call(this, directive)
diff --git a/package.json b/package.json
index a7eb62d..5285a01 100644
--- a/package.json
+++ b/package.json
@@ -63,10 +63,6 @@
   "xo": {
     "prettier": true,
     "rules": {
-      "no-var": "off",
-      "prefer-arrow-callback": "off",
-      "guard-for-in": "off",
-      "unicorn/explicit-length-check": "off",
       "unicorn/no-this-assignment": "off"
     }
   },
diff --git a/test/index.js b/test/index.js
index e6f1525..140d0a6 100644
--- a/test/index.js
+++ b/test/index.js
@@ -3,8 +3,10 @@ import {micromark} from 'micromark'
 import {htmlVoidElements} from 'html-void-elements'
 import {directive as syntax, directiveHtml as html} from '../index.js'
 
-test('micromark-extension-directive (syntax)', function (t) {
-  t.test('text', function (t) {
+const own = {}.hasOwnProperty
+
+test('micromark-extension-directive (syntax)', (t) => {
+  t.test('text', (t) => {
     t.equal(
       micromark('\\:a', options()),
       '<p>:a</p>',
@@ -362,7 +364,7 @@ test('micromark-extension-directive (syntax)', function (t) {
     t.end()
   })
 
-  t.test('leaf', function (t) {
+  t.test('leaf', (t) => {
     t.equal(micromark('::b', options()), '', 'should support a directive')
 
     t.equal(
@@ -696,7 +698,7 @@ test('micromark-extension-directive (syntax)', function (t) {
     t.end()
   })
 
-  t.test('container', function (t) {
+  t.test('container', (t) => {
     t.equal(micromark(':::b', options()), '', 'should support a directive')
 
     t.equal(
@@ -1103,7 +1105,7 @@ test('micromark-extension-directive (syntax)', function (t) {
   t.end()
 })
 
-test('micromark-extension-directive (compile)', function (t) {
+test('micromark-extension-directive (compile)', (t) => {
   t.equal(
     micromark(
       [
@@ -1179,7 +1181,7 @@ test('micromark-extension-directive (compile)', function (t) {
   t.end()
 })
 
-test('content', function (t) {
+test('content', (t) => {
   t.equal(
     micromark(':abbr[x\\&y&amp;z]', options({abbr})),
     '<p><abbr>x&amp;y&amp;z</abbr></p>',
@@ -1372,14 +1374,13 @@ function abbr(d) {
 }
 
 function youtube(d) {
-  var attrs = d.attributes || {}
-  var v = attrs.v
-  var list
-  var prop
+  const attrs = d.attributes || {}
+  const v = attrs.v
+  let prop
 
   if (!v) return false
 
-  list = [
+  const list = [
     'src="https://www.youtube.com/embed/' + this.encode(v) + '"',
     'allowfullscreen'
   ]
@@ -1406,17 +1407,19 @@ function youtube(d) {
 }
 
 function h(d) {
-  var content = d.content || d.label
-  var attrs = d.attributes || {}
-  var list = []
-  var prop
+  const content = d.content || d.label
+  const attrs = d.attributes || {}
+  const list = []
+  let prop
 
   for (prop in attrs) {
-    list.push(this.encode(prop) + '="' + this.encode(attrs[prop]) + '"')
+    if (own.call(attrs, prop)) {
+      list.push(this.encode(prop) + '="' + this.encode(attrs[prop]) + '"')
+    }
   }
 
   this.tag('<' + d.name)
-  if (list.length) this.tag(' ' + list.join(' '))
+  if (list.length > 0) this.tag(' ' + list.join(' '))
   this.tag('>')
 
   if (content) {