diff --git a/.github/workflows/bb.yml b/.github/workflows/bb.yml
index 291ab09..0198fc3 100644
--- a/.github/workflows/bb.yml
+++ b/.github/workflows/bb.yml
@@ -2,7 +2,7 @@ name: bb
 on:
   issues:
     types: [opened, reopened, edited, closed, labeled, unlabeled]
-  pull_request:
+  pull_request_target:
     types: [opened, reopened, edited, closed, labeled, unlabeled]
 jobs:
   main:
diff --git a/lib/any.js b/lib/any.js
index a1f9df0..2ceb1ff 100644
--- a/lib/any.js
+++ b/lib/any.js
@@ -17,19 +17,22 @@ import {pseudo} from './pseudo.js'
 import {test} from './test.js'
 import {root} from './util.js'
 
-var type = zwitch('type', {
+const type = zwitch('type', {
+  // @ts-expect-error: hush.
   unknown: unknownType,
   invalid: invalidType,
+  // @ts-expect-error: hush.
   handlers: {selectors, ruleSet, rule}
 })
 
 /**
  * @param {Selectors|RuleSet|Rule} query
- * @param {Node} node
+ * @param {Node|undefined} node
  * @param {SelectState} state
+ * @returns {Array.<Node>}
  */
 export function any(query, node, state) {
-  // @ts-ignore zwitch types are off.
+  // @ts-expect-error: fine.
   return query && node ? type(query, node, state) : []
 }
 
@@ -39,8 +42,8 @@ export function any(query, node, state) {
  * @param {SelectState} state
  */
 function selectors(query, node, state) {
-  var collect = collector(state.one)
-  var index = -1
+  const collect = collector(state.one)
+  let index = -1
 
   while (++index < query.selectors.length) {
     collect(ruleSet(query.selectors[index], node, state))
@@ -64,7 +67,7 @@ function ruleSet(query, node, state) {
  * @param {SelectState} state
  */
 function rule(query, tree, state) {
-  var collect = collector(state.one)
+  const collect = collector(state.one)
 
   if (state.shallow && query.rule) {
     throw new Error('Expected selector without nesting')
@@ -90,7 +93,7 @@ function rule(query, tree, state) {
   /** @type {SelectIterator} */
   function iterator(query, node, index, parent, state) {
     if (test(query, node, index, parent, state)) {
-      if ('rule' in query) {
+      if (query.rule) {
         nest(query.rule, node, index, parent, configure(query.rule, state))
       } else {
         collect(node)
@@ -107,8 +110,8 @@ function rule(query, tree, state) {
  * @returns {S}
  */
 function configure(query, state) {
-  var pseudos = query.pseudos || []
-  var index = -1
+  const pseudos = query.pseudos || []
+  let index = -1
 
   while (++index < pseudos.length) {
     if (pseudo.needsIndex.includes(pseudos[index].name)) {
@@ -136,13 +139,13 @@ function invalidType() {
 }
 
 /**
- * @param {boolean} one
+ * @param {boolean|undefined} one
  */
 function collector(one) {
   /** @type {Array.<Node>} */
-  var result = []
+  const result = []
   /** @type {boolean} */
-  var found
+  let found
 
   collect.result = result
 
@@ -154,7 +157,7 @@ function collector(one) {
    * @param {Node|Array.<Node>} node
    */
   function collect(node) {
-    var index = -1
+    let index = -1
 
     if ('length' in node) {
       while (++index < node.length) {
diff --git a/lib/attribute.js b/lib/attribute.js
index 124c56b..ec9f173 100644
--- a/lib/attribute.js
+++ b/lib/attribute.js
@@ -6,14 +6,21 @@
 
 import {zwitch} from 'zwitch'
 
-var handle = zwitch('operator', {
+const handle = zwitch('operator', {
+  // @ts-expect-error: hush.
   unknown: unknownOperator,
+  // @ts-expect-error: hush.
   invalid: exists,
   handlers: {
+    // @ts-expect-error: hush.
     '=': exact,
+    // @ts-expect-error: hush.
     '^=': begins,
+    // @ts-expect-error: hush.
     '$=': ends,
+    // @ts-expect-error: hush.
     '*=': containsString,
+    // @ts-expect-error: hush.
     '~=': containsArray
   }
 })
@@ -23,7 +30,7 @@ var handle = zwitch('operator', {
  * @param {Node} node
  */
 export function attribute(query, node) {
-  var index = -1
+  let index = -1
 
   while (++index < query.attrs.length) {
     if (!handle(query.attrs[index], node)) return false
@@ -39,6 +46,7 @@ export function attribute(query, node) {
  * @param {Node} node
  */
 function exists(query, node) {
+  // @ts-expect-error: Looks like a record.
   return node[query.name] !== null && node[query.name] !== undefined
 }
 
@@ -49,6 +57,7 @@ function exists(query, node) {
  * @param {Node} node
  */
 function exact(query, node) {
+  // @ts-expect-error: Looks like a record.
   return exists(query, node) && String(node[query.name]) === query.value
 }
 
@@ -59,7 +68,9 @@ function exact(query, node) {
  * @param {Node} node
  */
 function containsArray(query, node) {
-  var value = node[query.name]
+  /** @type {unknown} */
+  // @ts-expect-error: Looks like a record.
+  const value = node[query.name]
 
   if (value === null || value === undefined) return false
 
@@ -82,9 +93,12 @@ function containsArray(query, node) {
  * @param {Node} node
  */
 function begins(query, node) {
-  var value = node[query.name]
+  /** @type {unknown} */
+  // @ts-expect-error: Looks like a record.
+  const value = node[query.name]
 
   return (
+    query.value &&
     typeof value === 'string' &&
     value.slice(0, query.value.length) === query.value
   )
@@ -97,9 +111,12 @@ function begins(query, node) {
  * @param {Node} node
  */
 function ends(query, node) {
-  var value = node[query.name]
+  /** @type {unknown} */
+  // @ts-expect-error: Looks like a record.
+  const value = node[query.name]
 
   return (
+    query.value &&
     typeof value === 'string' &&
     value.slice(-query.value.length) === query.value
   )
@@ -112,8 +129,10 @@ function ends(query, node) {
  * @param {Node} node
  */
 function containsString(query, node) {
-  var value = node[query.name]
-  return typeof value === 'string' && value.includes(query.value)
+  /** @type {unknown} */
+  // @ts-expect-error: Looks like a record.
+  const value = node[query.name]
+  return query.value && typeof value === 'string' && value.includes(query.value)
 }
 
 // Shouldn’t be invoked, Parser throws an error instead.
diff --git a/lib/nest.js b/lib/nest.js
index 87221e6..fb3c905 100644
--- a/lib/nest.js
+++ b/lib/nest.js
@@ -11,23 +11,27 @@
 import {zwitch} from 'zwitch'
 import {parent} from './util.js'
 
-var own = {}.hasOwnProperty
+const own = {}.hasOwnProperty
 
-var handle = zwitch('nestingOperator', {
+const handle = zwitch('nestingOperator', {
+  // @ts-expect-error: hush.
   unknown: unknownNesting,
+  // @ts-expect-error: hush.
   invalid: topScan, // `undefined` is the top query selector.
   handlers: {
+    // @ts-expect-error: hush.
     null: descendant, // `null` is the descendant combinator.
+    // @ts-expect-error: hush.
     '>': child,
+    // @ts-expect-error: hush.
     '+': adjacentSibling,
+    // @ts-expect-error: hush.
     '~': generalSibling
   }
 })
 
 /** @type {Handler} */
-export function nest(query, node, index, parent, state) {
-  return handle(query, node, index, parent, state)
-}
+export const nest = handle
 
 // Shouldn’t be invoked, parser gives correct data.
 /* c8 ignore next 6 */
@@ -41,18 +45,34 @@ function unknownNesting(query) {
 /** @type {Handler} */
 function topScan(query, node, index, parent, state) {
   // Shouldn’t happen.
-  /* c8 ignore next 3 */
+  /* c8 ignore next 7 */
   if (parent) {
     throw new Error('topScan is supposed to be called from the root node')
   }
 
+  if (!state.iterator) {
+    throw new Error('Expected `iterator` to be defined')
+  }
+
+  // Shouldn’t happen.
+  /* c8 ignore next 3 */
+  if (typeof index !== 'number') {
+    throw new TypeError('Expected `index` to be defined')
+  }
+
   state.iterator(query, node, index, parent, state)
   if (!state.shallow) descendant(query, node, index, parent, state)
 }
 
 /** @type {Handler} */
 function descendant(query, node, index, parent, state) {
-  var previous = state.iterator
+  // Shouldn’t happen.
+  /* c8 ignore next 3 */
+  if (!state.iterator) {
+    throw new Error('Expected `iterator` to be defined')
+  }
+
+  const previous = state.iterator
 
   state.iterator = iterator
   child(query, node, index, parent, state)
@@ -79,6 +99,12 @@ function child(query, node, _1, _2, state) {
 
 /** @type {Handler} */
 function adjacentSibling(query, _, index, parent, state) {
+  // Shouldn’t happen.
+  /* c8 ignore next 3 */
+  if (typeof index !== 'number') {
+    throw new TypeError('Expected `index` to be defined')
+  }
+
   // Shouldn’t happen.
   /* c8 ignore next */
   if (!parent) return
@@ -92,6 +118,12 @@ function adjacentSibling(query, _, index, parent, state) {
 
 /** @type {Handler} */
 function generalSibling(query, _, index, parent, state) {
+  // Shouldn’t happen.
+  /* c8 ignore next 3 */
+  if (typeof index !== 'number') {
+    throw new TypeError('Expected `index` to be defined')
+  }
+
   // Shouldn’t happen.
   /* c8 ignore next */
   if (!parent) return
@@ -129,7 +161,7 @@ class WalkIterator {
    * @returns {this}
    */
   prefillTypeIndex(x, y) {
-    var [start, end] = this.defaults(x, y)
+    let [start, end] = this.defaults(x, y)
 
     if (this.typeIndex) {
       while (start < end) {
@@ -147,12 +179,12 @@ class WalkIterator {
    * @returns {this}
    */
   each(x, y) {
-    var [start, end] = this.defaults(x, y)
-    var child = this.parent.children[start]
+    const [start, end] = this.defaults(x, y)
+    const child = this.parent.children[start]
     /** @type {number} */
-    var index
+    let index
     /** @type {number} */
-    var nodeIndex
+    let nodeIndex
 
     if (start >= end) return this
 
@@ -161,6 +193,12 @@ class WalkIterator {
       index = this.typeIndex.index(child)
       this.delayed.push(delay)
     } else {
+      // Shouldn’t happen.
+      /* c8 ignore next 3 */
+      if (!this.state.iterator) {
+        throw new Error('Expected `iterator` to be defined')
+      }
+
       this.state.iterator(this.query, child, start, this.parent, this.state)
     }
 
@@ -173,6 +211,18 @@ class WalkIterator {
      * @this {WalkIterator}
      */
     function delay() {
+      // Shouldn’t happen.
+      /* c8 ignore next 3 */
+      if (!this.typeIndex) {
+        throw new TypeError('Expected `typeIndex` to be defined')
+      }
+
+      // Shouldn’t happen.
+      /* c8 ignore next 3 */
+      if (!this.state.iterator) {
+        throw new Error('Expected `iterator` to be defined')
+      }
+
       this.state.typeIndex = index
       this.state.nodeIndex = nodeIndex
       this.state.typeCount = this.typeIndex.count(child)
@@ -186,7 +236,7 @@ class WalkIterator {
    * @returns {this}
    */
   done() {
-    var index = -1
+    let index = -1
 
     while (++index < this.delayed.length) {
       this.delayed[index].call(this)
@@ -222,7 +272,7 @@ class TypeIndex {
    * @returns {number}
    */
   index(node) {
-    var type = node.type
+    const type = node.type
 
     this.nodes++
 
diff --git a/lib/parse.js b/lib/parse.js
index 2ada1d6..738e7c5 100644
--- a/lib/parse.js
+++ b/lib/parse.js
@@ -12,23 +12,24 @@ import fauxEsmNthCheck from 'nth-check'
 import {zwitch} from 'zwitch'
 
 /** @type {import('nth-check').default} */
-// @ts-ignore
-var nthCheck = fauxEsmNthCheck.default
+// @ts-expect-error
+const nthCheck = fauxEsmNthCheck.default
 
-var nth = new Set([
+const nth = new Set([
   'nth-child',
   'nth-last-child',
   'nth-of-type',
   'nth-last-of-type'
 ])
 
-var parser = new CssSelectorParser()
+const parser = new CssSelectorParser()
 
 parser.registerAttrEqualityMods('~', '^', '$', '*')
 parser.registerSelectorPseudos('any', 'matches', 'not', 'has')
 parser.registerNestingOperators('>', '+', '~')
 
-var compile = zwitch('type', {handlers: {selectors, ruleSet, rule}})
+// @ts-expect-error: hush.
+const compile = zwitch('type', {handlers: {selectors, ruleSet, rule}})
 
 /**
  * @param {string} selector
@@ -39,7 +40,7 @@ export function parse(selector) {
     throw new TypeError('Expected `string` as selector, not `' + selector + '`')
   }
 
-  // @ts-ignore types are wrong.
+  // @ts-expect-error types are wrong.
   return compile(parser.parse(selector))
 }
 
@@ -47,8 +48,8 @@ export function parse(selector) {
  * @param {Selectors} query
  */
 function selectors(query) {
-  var selectors = query.selectors
-  var index = -1
+  const selectors = query.selectors
+  let index = -1
 
   while (++index < selectors.length) {
     compile(selectors[index])
@@ -68,18 +69,18 @@ function ruleSet(query) {
  * @param {Rule} query
  */
 function rule(query) {
-  var pseudos = query.pseudos || []
-  var index = -1
+  const pseudos = query.pseudos || []
+  let index = -1
   /** @type {RulePseudo|RulePseudoNth} */
-  var pseudo
+  let pseudo
 
   while (++index < pseudos.length) {
     pseudo = pseudos[index]
 
     if (nth.has(pseudo.name)) {
-      // @ts-ignore Patch a non-primitive type.
+      // @ts-expect-error Patch a non-primitive type.
       pseudo.value = nthCheck(pseudo.value)
-      // @ts-ignore Patch a non-primitive type.
+      // @ts-expect-error Patch a non-primitive type.
       pseudo.valueType = 'function'
     }
   }
diff --git a/lib/pseudo.js b/lib/pseudo.js
index 55f5536..134ab91 100644
--- a/lib/pseudo.js
+++ b/lib/pseudo.js
@@ -14,29 +14,48 @@ import {zwitch} from 'zwitch'
 import {convert} from 'unist-util-is'
 import {parent} from './util.js'
 
-var is = convert()
+const is = convert()
 
-var handle = zwitch('name', {
+const handle = zwitch('name', {
+  // @ts-expect-error: hush.
   unknown: unknownPseudo,
   invalid: invalidPseudo,
   handlers: {
+    // @ts-expect-error: hush.
     any: matches,
+    // @ts-expect-error: hush.
     blank: empty,
+    // @ts-expect-error: hush.
     empty,
+    // @ts-expect-error: hush.
     'first-child': firstChild,
+    // @ts-expect-error: hush.
     'first-of-type': firstOfType,
+    // @ts-expect-error: hush.
     has: hasSelector,
+    // @ts-expect-error: hush.
     'last-child': lastChild,
+    // @ts-expect-error: hush.
     'last-of-type': lastOfType,
+    // @ts-expect-error: hush.
     matches,
+    // @ts-expect-error: hush.
     not,
+    // @ts-expect-error: hush.
     'nth-child': nthChild,
+    // @ts-expect-error: hush.
     'nth-last-child': nthLastChild,
+    // @ts-expect-error: hush.
     'nth-of-type': nthOfType,
+    // @ts-expect-error: hush.
     'nth-last-of-type': nthLastOfType,
+    // @ts-expect-error: hush.
     'only-child': onlyChild,
+    // @ts-expect-error: hush.
     'only-of-type': onlyOfType,
+    // @ts-expect-error: hush.
     root,
+    // @ts-expect-error: hush.
     scope
   }
 })
@@ -63,8 +82,8 @@ pseudo.needsIndex = [
  * @returns {boolean}
  */
 export function pseudo(query, node, index, parent, state) {
-  var pseudos = query.pseudos
-  var offset = -1
+  const pseudos = query.pseudos
+  let offset = -1
 
   while (++offset < pseudos.length) {
     if (!handle(pseudos[offset], node, index, parent, state)) return false
@@ -82,15 +101,13 @@ export function pseudo(query, node, index, parent, state) {
  * @returns {boolean}
  */
 function matches(query, node, _1, _2, state) {
-  var shallow = state.shallow
-  var one = state.one
-  /** @type {boolean} */
-  var result
+  const shallow = state.shallow
+  const one = state.one
 
   state.one = true
   state.shallow = true
 
-  result = state.any(query.value, node, state)[0] === node
+  const result = state.any(query.value, node, state)[0] === node
 
   state.shallow = shallow
   state.one = one
@@ -130,7 +147,11 @@ function root(_1, node, _2, parent) {
  * @returns {boolean}
  */
 function scope(_1, node, _2, _3, state) {
-  return is(node) && state.scopeNodes.includes(node)
+  return (
+    is(node) &&
+    state.scopeNodes !== undefined &&
+    state.scopeNodes.includes(node)
+  )
 }
 
 /**
@@ -165,7 +186,10 @@ function firstChild(query, _1, _2, _3, state) {
  */
 function lastChild(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return state.nodeIndex === state.nodeCount - 1
+  return (
+    typeof state.nodeCount === 'number' &&
+    state.nodeIndex === state.nodeCount - 1
+  )
 }
 
 /**
@@ -191,7 +215,7 @@ function onlyChild(query, _1, _2, _3, state) {
  */
 function nthChild(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return query.value(state.nodeIndex)
+  return typeof state.nodeIndex === 'number' && query.value(state.nodeIndex)
 }
 
 /**
@@ -204,7 +228,11 @@ function nthChild(query, _1, _2, _3, state) {
  */
 function nthLastChild(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return query.value(state.nodeCount - state.nodeIndex - 1)
+  return (
+    typeof state.nodeCount === 'number' &&
+    typeof state.nodeIndex === 'number' &&
+    query.value(state.nodeCount - state.nodeIndex - 1)
+  )
 }
 
 /**
@@ -217,7 +245,7 @@ function nthLastChild(query, _1, _2, _3, state) {
  */
 function nthOfType(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return query.value(state.typeIndex)
+  return typeof state.typeIndex === 'number' && query.value(state.typeIndex)
 }
 
 /**
@@ -230,7 +258,11 @@ function nthOfType(query, _1, _2, _3, state) {
  */
 function nthLastOfType(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return query.value(state.typeCount - 1 - state.typeIndex)
+  return (
+    typeof state.typeIndex === 'number' &&
+    typeof state.typeCount === 'number' &&
+    query.value(state.typeCount - 1 - state.typeIndex)
+  )
 }
 
 /**
@@ -256,7 +288,10 @@ function firstOfType(query, _1, _2, _3, state) {
  */
 function lastOfType(query, _1, _2, _3, state) {
   assertDeep(state, query)
-  return state.typeIndex === state.typeCount - 1
+  return (
+    typeof state.typeCount === 'number' &&
+    state.typeIndex === state.typeCount - 1
+  )
 }
 
 /**
@@ -309,19 +344,17 @@ function assertDeep(state, query) {
  * @returns {boolean}
  */
 function hasSelector(query, node, _1, _2, state) {
-  var shallow = state.shallow
-  var one = state.one
-  var scopeNodes = state.scopeNodes
-  var value = appendScope(query.value)
-  var anything = state.any
-  /** @type {boolean} */
-  var result
+  const shallow = state.shallow
+  const one = state.one
+  const scopeNodes = state.scopeNodes
+  const value = appendScope(query.value)
+  const anything = state.any
 
   state.shallow = false
   state.one = true
   state.scopeNodes = [node]
 
-  result = Boolean(anything(value, node, state)[0])
+  const result = Boolean(anything(value, node, state)[0])
 
   state.shallow = shallow
   state.one = one
@@ -335,11 +368,11 @@ function hasSelector(query, node, _1, _2, state) {
  */
 function appendScope(value) {
   /** @type {Selectors} */
-  var selector =
+  const selector =
     value.type === 'ruleSet' ? {type: 'selectors', selectors: [value]} : value
-  var index = -1
+  let index = -1
   /** @type {Rule} */
-  var rule
+  let rule
 
   while (++index < selector.selectors.length) {
     rule = selector.selectors[index].rule
@@ -358,7 +391,7 @@ function appendScope(value) {
         rule: {
           type: 'rule',
           rule,
-          // @ts-ignore pseudos are fine w/ just a name!
+          // @ts-expect-error pseudos are fine w/ just a name!
           pseudos: [{name: 'scope'}]
         }
       }
diff --git a/lib/types.js b/lib/types.js
index 1d5fb2f..0f92669 100644
--- a/lib/types.js
+++ b/lib/types.js
@@ -30,9 +30,9 @@
  * @typedef {import('unist').Parent} Parent
  *
  * @typedef {Object} SelectState
- * @property {(query: Query, node: Node, state: SelectState) => Node[]} any
+ * @property {(query: Selectors|RuleSet|Rule, node: Node|undefined, state: SelectState) => Node[]} any
  * @property {Array.<Node>} [scopeNodes]
- * @property {SelectIterator} [iterator]
+ * @property {SelectIterator|null|undefined} [iterator]
  * @property {boolean} [one=false]
  * @property {boolean} [shallow=false]
  * @property {boolean} [index=false]
diff --git a/lib/util.js b/lib/util.js
index 49a92ff..4986750 100644
--- a/lib/util.js
+++ b/lib/util.js
@@ -29,5 +29,6 @@ export function root(node) {
  * @returns {node is Parent}
  */
 export function parent(node) {
+  // @ts-expect-error: looks like a record.
   return Array.isArray(node.children)
 }
diff --git a/package.json b/package.json
index 25dd667..cb52a38 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "unist-util-select",
-  "version": "4.0.0",
+  "version": "4.0.1",
   "description": "unist utility to select nodes with CSS-like selectors",
   "license": "MIT",
   "keywords": [
@@ -48,6 +48,7 @@
     "index.js"
   ],
   "dependencies": {
+    "@types/unist": "^2.0.0",
     "css-selector-parser": "^1.0.0",
     "nth-check": "^2.0.0",
     "unist-util-is": "^5.0.0",
@@ -57,14 +58,14 @@
     "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "prettier": "^2.0.0",
-    "remark-cli": "^9.0.0",
-    "remark-preset-wooorm": "^8.0.0",
+    "remark-cli": "^10.0.0",
+    "remark-preset-wooorm": "^9.0.0",
     "rimraf": "^3.0.0",
     "tape": "^5.0.0",
     "type-coverage": "^2.0.0",
     "typescript": "^4.0.0",
     "unist-builder": "^3.0.0",
-    "xo": "^0.38.0"
+    "xo": "^0.46.0"
   },
   "scripts": {
     "prepack": "npm run build && npm run format",
@@ -85,10 +86,7 @@
   "xo": {
     "prettier": true,
     "rules": {
-      "no-var": "off",
-      "prefer-arrow-callback": "off",
-      "max-params": "off",
-      "unicorn/no-array-for-each": "off"
+      "max-params": "off"
     }
   },
   "remarkConfig": {
diff --git a/test/all.js b/test/all.js
index 7d6ce9c..edeb4f8 100644
--- a/test/all.js
+++ b/test/all.js
@@ -2,7 +2,7 @@ import test from 'tape'
 import {u} from 'unist-builder'
 import {selectAll} from '../index.js'
 
-test('all together now', function (t) {
+test('all together now', (t) => {
   t.deepEqual(
     selectAll(
       'a > b[d]:nth-of-type(odd)',
diff --git a/test/matches.js b/test/matches.js
index 9c79128..3793b53 100644
--- a/test/matches.js
+++ b/test/matches.js
@@ -1,12 +1,16 @@
+/**
+ * @typedef {import('unist').Literal<string>} Literal
+ */
+
 import test from 'tape'
 import {u} from 'unist-builder'
 import {matches} from '../index.js'
 
-test('select.matches()', function (t) {
-  t.test('invalid selector', function (st) {
+test('select.matches()', (t) => {
+  t.test('invalid selector', (st) => {
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         matches()
       },
       /Error: Expected `string` as selector, not `undefined`/,
@@ -14,8 +18,8 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         matches([], u('root', []))
       },
       /Error: Expected `string` as selector, not ``/,
@@ -23,7 +27,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches('@supports (transform-origin: 5% 5%) {}', u('root', []))
       },
       /Error: Rule expected but "@" found./,
@@ -31,7 +35,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches('[foo%=bar]', u('root', []))
       },
       /Error: Expected "=" but "%" found./,
@@ -39,7 +43,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches(':active', u('root', []))
       },
       /Error: Unknown pseudo-selector `active`/,
@@ -47,7 +51,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches(':nth-foo(2n+1)', u('root', []))
       },
       /Error: Unknown pseudo-selector `nth-foo`/,
@@ -55,7 +59,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches('::before', u('root', []))
       },
       /Error: Unexpected pseudo-element or empty pseudo-class/,
@@ -63,7 +67,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches('foo bar', u('root', []))
       },
       /Error: Expected selector without nesting/,
@@ -71,7 +75,7 @@ test('select.matches()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         matches('foo > bar', u('root', []))
       },
       /Error: Expected selector without nesting/,
@@ -81,8 +85,8 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('parent-sensitive pseudo-selectors', function (st) {
-    var simplePseudos = [
+  t.test('parent-sensitive pseudo-selectors', (st) => {
+    const simplePseudos = [
       'first-child',
       'first-of-type',
       'last-child',
@@ -91,37 +95,45 @@ test('select.matches()', function (t) {
       'only-of-type'
     ]
 
-    var functionalPseudos = [
+    const functionalPseudos = [
       'nth-child',
       'nth-last-child',
       'nth-of-type',
       'nth-last-of-type'
     ]
 
-    simplePseudos.forEach(function (pseudo) {
+    let index = -1
+
+    while (++index < simplePseudos.length) {
+      const pseudo = simplePseudos[index]
+
       st.throws(
-        function () {
+        () => {
           matches(':' + pseudo, u('root', []))
         },
         new RegExp('Error: Cannot use `:' + pseudo + '` without parent'),
         'should throw on `' + pseudo + '`'
       )
-    })
+    }
+
+    index = -1
+
+    while (++index < functionalPseudos.length) {
+      const pseudo = functionalPseudos[index]
 
-    functionalPseudos.forEach(function (pseudo) {
       st.throws(
-        function () {
+        () => {
           matches(':' + pseudo + '()', u('root', []))
         },
-        new RegExp('Error: Cannot use `:' + pseudo + '` without parent'),
+        /n-th rule couldn't be parsed/,
         'should throw on `' + pseudo + '()`'
       )
-    })
+    }
 
     st.end()
   })
 
-  t.test('general', function (st) {
+  t.test('general', (st) => {
     st.notOk(
       matches('', u('root', [])),
       'false for the empty string as selector'
@@ -131,19 +143,22 @@ test('select.matches()', function (t) {
       'false for a white-space only selector'
     )
     st.notOk(matches('*'), 'false if not given a node')
-    st.ok(matches('*', {type: 'text', value: 'a'}), 'true if given an node')
+    st.ok(
+      matches('*', /** @type {Literal} */ ({type: 'text', value: 'a'})),
+      'true if given an node'
+    )
 
     st.end()
   })
 
-  t.test('multiple selectors', function (st) {
+  t.test('multiple selectors', (st) => {
     st.ok(matches('a, b', u('a')), 'true')
     st.notOk(matches('b, c', u('a')), 'false')
 
     st.end()
   })
 
-  t.test('tag-names: `div`, `*`', function (st) {
+  t.test('tag-names: `div`, `*`', (st) => {
     st.ok(matches('*', u('a')), 'true for `*`')
     st.ok(matches('b', u('b')), 'true if types matches')
     st.notOk(matches('b', u('a')), 'false if types don’t matches')
@@ -151,9 +166,9 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('id: `#id`', function (st) {
+  t.test('id: `#id`', (st) => {
     st.throws(
-      function () {
+      () => {
         matches('#one', u('a'))
       },
       /Error: Invalid selector: id/,
@@ -163,9 +178,9 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('class: `.class`', function (st) {
+  t.test('class: `.class`', (st) => {
     st.throws(
-      function () {
+      () => {
         matches('.one', u('a'))
       },
       /Error: Invalid selector: class/,
@@ -175,7 +190,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, existence: `[attr]`', function (st) {
+  t.test('attributes, existence: `[attr]`', (st) => {
     st.ok(
       matches('[foo]', u('a', {foo: 'alpha'})),
       'true if attribute exists (string)'
@@ -208,7 +223,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, equality: `[attr=value]`', function (st) {
+  t.test('attributes, equality: `[attr=value]`', (st) => {
     st.ok(
       matches('[foo=alpha]', u('a', {foo: 'alpha'})),
       'true if attribute matches (string)'
@@ -270,7 +285,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, begins: `[attr^=value]`', function (st) {
+  t.test('attributes, begins: `[attr^=value]`', (st) => {
     st.ok(
       matches('[foo^=al]', u('a', {foo: 'alpha'})),
       'true if attribute matches (string)'
@@ -300,7 +315,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, ends: `[attr$=value]`', function (st) {
+  t.test('attributes, ends: `[attr$=value]`', (st) => {
     st.ok(
       matches('[foo$=ha]', u('a', {foo: 'alpha'})),
       'true if attribute matches (string)'
@@ -330,7 +345,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, contains: `[attr*=value]`', function (st) {
+  t.test('attributes, contains: `[attr*=value]`', (st) => {
     st.ok(
       matches('[foo*=ph]', u('a', {foo: 'alpha'})),
       'true if attribute matches (string)'
@@ -359,7 +374,7 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('attributes, contains in a list: `[attr~=value]`', function (st) {
+  t.test('attributes, contains in a list: `[attr~=value]`', (st) => {
     st.ok(
       matches('[foo~=alpha]', u('a', {foo: 'alpha'})),
       'true if attribute matches (string)'
@@ -437,9 +452,14 @@ test('select.matches()', function (t) {
     st.end()
   })
 
-  t.test('pseudo-classes', function (st) {
-    ;[':any', ':matches'].forEach(function (pseudo) {
-      st.test(pseudo, function (sst) {
+  t.test('pseudo-classes', (st) => {
+    const anyMatchesPseudos = [':any', ':matches']
+    let index = -1
+
+    while (++index < anyMatchesPseudos.length) {
+      const pseudo = anyMatchesPseudos[index]
+
+      st.test(pseudo, (sst) => {
         sst.ok(
           matches(pseudo + '(a, [b])', u('a')),
           'true if any matches (type)'
@@ -459,9 +479,9 @@ test('select.matches()', function (t) {
 
         sst.end()
       })
-    })
+    }
 
-    st.test(':not()', function (sst) {
+    st.test(':not()', (sst) => {
       sst.notOk(matches(':not(a, [b])', u('a')), 'false if any matches (type)')
       sst.notOk(
         matches(':not(a, [b])', u('c', {b: 1})),
@@ -476,12 +496,12 @@ test('select.matches()', function (t) {
       sst.end()
     })
 
-    st.test(':has', function (sst) {
-      sst.doesNotThrow(function () {
+    st.test(':has', (sst) => {
+      sst.doesNotThrow(() => {
         matches('a:not(:has())', u('b'))
       }, 'should not throw on empty selectors')
 
-      sst.doesNotThrow(function () {
+      sst.doesNotThrow(() => {
         matches('a:has()', u('b'))
       }, 'should not throw on empty selectors')
 
@@ -583,8 +603,15 @@ test('select.matches()', function (t) {
 
       sst.end()
     })
-    ;[':empty', ':blank'].forEach(function (pseudo) {
-      st.test(pseudo, function (sst) {
+
+    const emptyBlankPseudos = [':empty', ':blank']
+
+    index = -1
+
+    while (++index < emptyBlankPseudos.length) {
+      const pseudo = emptyBlankPseudos[index]
+
+      st.test(pseudo, (sst) => {
         sst.ok(matches(pseudo, u('a')), 'true for void node')
         sst.ok(matches(pseudo, u('a', [])), 'true for parent without children')
         sst.notOk(matches(pseudo, u('a', '')), 'false for falsey literal')
@@ -593,14 +620,14 @@ test('select.matches()', function (t) {
 
         sst.end()
       })
-    })
+    }
 
-    st.test(':root', function (sst) {
+    st.test(':root', (sst) => {
       sst.ok(matches(':root', u('a')), 'true')
       sst.end()
     })
 
-    st.test(':scope', function (sst) {
+    st.test(':scope', (sst) => {
       sst.ok(matches(':scope', u('a')), 'true')
       sst.end()
     })
diff --git a/test/select-all.js b/test/select-all.js
index 7b67e54..04d58a9 100644
--- a/test/select-all.js
+++ b/test/select-all.js
@@ -2,11 +2,11 @@ import test from 'tape'
 import {u} from 'unist-builder'
 import {selectAll} from '../index.js'
 
-test('select.selectAll()', function (t) {
-  t.test('invalid selectors', function (st) {
+test('select.selectAll()', (t) => {
+  t.test('invalid selectors', (st) => {
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         selectAll()
       },
       /Error: Expected `string` as selector, not `undefined`/,
@@ -14,8 +14,8 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         selectAll([], u('a'))
       },
       /Error: Expected `string` as selector, not ``/,
@@ -23,7 +23,7 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         selectAll('@supports (transform-origin: 5% 5%) {}', u('a'))
       },
       /Error: Rule expected but "@" found./,
@@ -31,7 +31,7 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         selectAll('[foo%=bar]', u('a'))
       },
       /Error: Expected "=" but "%" found./,
@@ -39,7 +39,7 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         selectAll(':active', u('a'))
       },
       /Error: Unknown pseudo-selector `active`/,
@@ -47,7 +47,7 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         selectAll(':nth-foo(2n+1)', u('a'))
       },
       /Error: Unknown pseudo-selector `nth-foo`/,
@@ -55,7 +55,7 @@ test('select.selectAll()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         selectAll('::before', u('a'))
       },
       /Error: Unexpected pseudo-element or empty pseudo-class/,
@@ -65,7 +65,7 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('general', function (st) {
+  t.test('general', (st) => {
     st.deepEqual(
       selectAll('', u('a')),
       [],
@@ -82,7 +82,7 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('descendant selector', function (st) {
+  t.test('descendant selector', (st) => {
     st.deepEqual(
       selectAll(
         'b',
@@ -132,7 +132,7 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('child selector', function (st) {
+  t.test('child selector', (st) => {
     st.deepEqual(
       selectAll(
         'c > d',
@@ -165,7 +165,7 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('adjacent sibling selector', function (st) {
+  t.test('adjacent sibling selector', (st) => {
     st.deepEqual(
       selectAll(
         'c + b',
@@ -198,7 +198,7 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('general sibling selector', function (st) {
+  t.test('general sibling selector', (st) => {
     st.deepEqual(
       selectAll(
         'c ~ b',
@@ -240,8 +240,8 @@ test('select.selectAll()', function (t) {
     st.end()
   })
 
-  t.test('parent-sensitive pseudo-selectors', function (st) {
-    st.test(':first-child', function (sst) {
+  t.test('parent-sensitive pseudo-selectors', (st) => {
+    st.test(':first-child', (sst) => {
       sst.deepEqual(
         selectAll(
           ':first-child',
@@ -278,7 +278,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':last-child', function (sst) {
+    st.test(':last-child', (sst) => {
       sst.deepEqual(
         selectAll(
           ':last-child',
@@ -315,7 +315,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':only-child', function (sst) {
+    st.test(':only-child', (sst) => {
       sst.deepEqual(
         selectAll(
           ':only-child',
@@ -343,7 +343,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-child', function (sst) {
+    st.test(':nth-child', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:nth-child(odd)',
@@ -411,7 +411,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-last-child', function (sst) {
+    st.test(':nth-last-child', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:nth-last-child(odd)',
@@ -479,7 +479,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-of-type', function (sst) {
+    st.test(':nth-of-type', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:nth-of-type(odd)',
@@ -547,7 +547,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-last-of-type', function (sst) {
+    st.test(':nth-last-of-type', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:nth-last-of-type(odd)',
@@ -615,7 +615,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':first-of-type', function (sst) {
+    st.test(':first-of-type', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:first-of-type',
@@ -641,7 +641,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':last-of-type', function (sst) {
+    st.test(':last-of-type', (sst) => {
       sst.deepEqual(
         selectAll(
           'b:last-of-type',
@@ -667,7 +667,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':only-of-type', function (sst) {
+    st.test(':only-of-type', (sst) => {
       sst.deepEqual(
         selectAll(
           'c:only-of-type',
@@ -707,7 +707,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':root', function (sst) {
+    st.test(':root', (sst) => {
       sst.deepEqual(
         selectAll(':root', u('a', [u('b'), u('c', [u('d')])])),
         [u('a', [u('b'), u('c', [u('d')])])],
@@ -717,7 +717,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':scope', function (sst) {
+    st.test(':scope', (sst) => {
       sst.deepEqual(
         selectAll(':scope', u('a', [u('b'), u('c', [u('d')])])),
         [u('a', [u('b'), u('c', [u('d')])])],
@@ -727,7 +727,7 @@ test('select.selectAll()', function (t) {
       sst.end()
     })
 
-    st.test(':has', function (sst) {
+    st.test(':has', (sst) => {
       sst.deepEqual(
         selectAll('c:has(:first-child)', u('a', [u('b'), u('c', [u('d')])])),
         [u('c', [u('d')])],
diff --git a/test/select.js b/test/select.js
index 0307688..306bb69 100644
--- a/test/select.js
+++ b/test/select.js
@@ -2,11 +2,11 @@ import test from 'tape'
 import {u} from 'unist-builder'
 import {select} from '../index.js'
 
-test('select.select()', function (t) {
-  t.test('invalid selectors', function (st) {
+test('select.select()', (t) => {
+  t.test('invalid selectors', (st) => {
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         select()
       },
       /Error: Expected `string` as selector, not `undefined`/,
@@ -14,8 +14,8 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
-        // @ts-ignore runtime.
+      () => {
+        // @ts-expect-error runtime.
         select([], u('a'))
       },
       /Error: Expected `string` as selector, not ``/,
@@ -23,7 +23,7 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         select('@supports (transform-origin: 5% 5%) {}', u('a'))
       },
       /Error: Rule expected but "@" found./,
@@ -31,7 +31,7 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         select('[foo%=bar]', u('a'))
       },
       /Error: Expected "=" but "%" found./,
@@ -39,7 +39,7 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         select(':active', u('a'))
       },
       /Error: Unknown pseudo-selector `active`/,
@@ -47,7 +47,7 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         select(':nth-foo(2n+1)', u('a'))
       },
       /Error: Unknown pseudo-selector `nth-foo`/,
@@ -55,7 +55,7 @@ test('select.select()', function (t) {
     )
 
     st.throws(
-      function () {
+      () => {
         select('::before', u('a'))
       },
       /Error: Unexpected pseudo-element or empty pseudo-class/,
@@ -65,7 +65,7 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('general', function (st) {
+  t.test('general', (st) => {
     st.equal(
       select('', u('a')),
       null,
@@ -83,7 +83,7 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('descendant selector', function (st) {
+  t.test('descendant selector', (st) => {
     st.deepEqual(
       select(
         'b',
@@ -122,7 +122,7 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('child selector', function (st) {
+  t.test('child selector', (st) => {
     st.deepEqual(
       select('c > e', u('a', [u('b'), u('c', [u('d'), u('e', [u('f')])])])),
       u('e', [u('f')]),
@@ -149,7 +149,7 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('adjacent sibling selector', function (st) {
+  t.test('adjacent sibling selector', (st) => {
     st.deepEqual(
       select(
         'c + b',
@@ -182,7 +182,7 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('general sibling selector', function (st) {
+  t.test('general sibling selector', (st) => {
     st.deepEqual(
       select(
         'c ~ b',
@@ -224,8 +224,8 @@ test('select.select()', function (t) {
     st.end()
   })
 
-  t.test('parent-sensitive pseudo-selectors', function (st) {
-    st.test(':first-child', function (sst) {
+  t.test('parent-sensitive pseudo-selectors', (st) => {
+    st.test(':first-child', (sst) => {
       sst.deepEqual(
         select(
           ':first-child',
@@ -253,7 +253,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':last-child', function (sst) {
+    st.test(':last-child', (sst) => {
       sst.deepEqual(
         select(
           ':last-child',
@@ -281,7 +281,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':only-child', function (sst) {
+    st.test(':only-child', (sst) => {
       sst.deepEqual(
         select(
           ':only-child',
@@ -309,7 +309,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-child', function (sst) {
+    st.test(':nth-child', (sst) => {
       sst.deepEqual(
         select(
           'b:nth-child(odd)',
@@ -377,7 +377,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-last-child', function (sst) {
+    st.test(':nth-last-child', (sst) => {
       sst.deepEqual(
         select(
           'b:nth-last-child(odd)',
@@ -445,7 +445,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-of-type', function (sst) {
+    st.test(':nth-of-type', (sst) => {
       sst.deepEqual(
         select(
           'b:nth-of-type(odd)',
@@ -513,7 +513,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':nth-last-of-type', function (sst) {
+    st.test(':nth-last-of-type', (sst) => {
       sst.deepEqual(
         select(
           'b:nth-last-of-type(odd)',
@@ -581,7 +581,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':first-of-type', function (sst) {
+    st.test(':first-of-type', (sst) => {
       sst.deepEqual(
         select(
           'b:first-of-type',
@@ -607,7 +607,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':last-of-type', function (sst) {
+    st.test(':last-of-type', (sst) => {
       sst.deepEqual(
         select(
           'b:last-of-type',
@@ -633,7 +633,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':only-of-type', function (sst) {
+    st.test(':only-of-type', (sst) => {
       sst.deepEqual(
         select(
           'c:only-of-type',
@@ -673,7 +673,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':root', function (sst) {
+    st.test(':root', (sst) => {
       sst.deepEqual(
         select(':root', u('a', [u('b'), u('c', [u('d')])])),
         u('a', [u('b'), u('c', [u('d')])]),
@@ -683,7 +683,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':scope', function (sst) {
+    st.test(':scope', (sst) => {
       sst.deepEqual(
         select(':scope', u('a', [u('b'), u('c', [u('d')])])),
         u('a', [u('b'), u('c', [u('d')])]),
@@ -693,7 +693,7 @@ test('select.select()', function (t) {
       sst.end()
     })
 
-    st.test(':has', function (sst) {
+    st.test(':has', (sst) => {
       sst.deepEqual(
         select('c:has(:first-child)', u('a', [u('b'), u('c', [u('d')])])),
         u('c', [u('d')]),
diff --git a/tsconfig.json b/tsconfig.json
index 2b103bd..f437d29 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -10,6 +10,7 @@
     "declaration": true,
     "emitDeclarationOnly": true,
     "allowSyntheticDefaultImports": true,
-    "skipLibCheck": true
+    "skipLibCheck": true,
+    "strict": true
   }
 }