diff --git a/.gitignore b/.gitignore
index f394799..c77b50d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,9 +1,6 @@
 .DS_Store
 *.log
-.nyc_output/
 coverage/
 node_modules/
 test/jsx-*.js
-hastscript.js
-hastscript.min.js
 yarn.lock
diff --git a/.prettierignore b/.prettierignore
index c50edf1..cebe81f 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,5 +1,2 @@
 coverage/
-hastscript.js
-hastscript.min.js
-*.json
 *.md
diff --git a/factory.js b/factory.js
deleted file mode 100644
index cc39c38..0000000
--- a/factory.js
+++ /dev/null
@@ -1,193 +0,0 @@
-'use strict'
-
-var find = require('property-information/find')
-var normalize = require('property-information/normalize')
-var parseSelector = require('hast-util-parse-selector')
-var spaceSeparated = require('space-separated-tokens')
-var commaSeparated = require('comma-separated-tokens')
-
-module.exports = factory
-
-var own = {}.hasOwnProperty
-
-function factory(schema, defaultTagName, caseSensitive) {
-  var adjust = caseSensitive && createAdjustMap(caseSensitive)
-
-  return h
-
-  // Hyperscript compatible DSL for creating virtual hast trees.
-  function h(selector, properties) {
-    var node =
-      selector == null
-        ? {type: 'root', children: []}
-        : parseSelector(selector, defaultTagName)
-    var name = selector == null ? null : node.tagName.toLowerCase()
-    var index = 1
-    var property
-
-    // Normalize the name.
-    if (name != null) {
-      node.tagName = adjust && own.call(adjust, name) ? adjust[name] : name
-    }
-
-    // Handle props.
-    if (properties) {
-      if (
-        name == null ||
-        typeof properties === 'string' ||
-        'length' in properties ||
-        isNode(name, properties)
-      ) {
-        // Nope, it’s something for `children`.
-        index--
-      } else {
-        for (property in properties) {
-          addProperty(schema, node.properties, property, properties[property])
-        }
-      }
-    }
-
-    // Handle children.
-    while (++index < arguments.length) {
-      addChild(node.children, arguments[index])
-    }
-
-    if (name === 'template') {
-      node.content = {type: 'root', children: node.children}
-      node.children = []
-    }
-
-    return node
-  }
-}
-
-function isNode(name, value) {
-  var type = value.type
-
-  if (name === 'input' || !type || typeof type !== 'string') {
-    return false
-  }
-
-  if (typeof value.children === 'object' && 'length' in value.children) {
-    return true
-  }
-
-  type = type.toLowerCase()
-
-  if (name === 'button') {
-    return (
-      type !== 'menu' &&
-      type !== 'submit' &&
-      type !== 'reset' &&
-      type !== 'button'
-    )
-  }
-
-  return 'value' in value
-}
-
-function addProperty(schema, properties, key, value) {
-  var info = find(schema, key)
-  var result = value
-  var index = -1
-  var finalResult
-
-  // Ignore nullish and NaN values.
-  if (result == null || result !== result) {
-    return
-  }
-
-  // Handle list values.
-  if (typeof result === 'string') {
-    if (info.spaceSeparated) {
-      result = spaceSeparated.parse(result)
-    } else if (info.commaSeparated) {
-      result = commaSeparated.parse(result)
-    } else if (info.commaOrSpaceSeparated) {
-      result = spaceSeparated.parse(commaSeparated.parse(result).join(' '))
-    }
-  }
-
-  // Accept `object` on style.
-  if (info.property === 'style' && typeof result !== 'string') {
-    result = style(result)
-  }
-
-  // Class names (which can be added both on the `selector` and here).
-  if (info.property === 'className' && properties.className) {
-    result = properties.className.concat(result)
-  }
-
-  if (typeof result === 'object' && 'length' in result) {
-    finalResult = []
-    while (++index < result.length) {
-      finalResult[index] = parsePrimitive(info, info.property, result[index])
-    }
-  } else {
-    finalResult = parsePrimitive(info, info.property, result)
-  }
-
-  properties[info.property] = finalResult
-}
-
-function addChild(nodes, value) {
-  var index = -1
-
-  if (typeof value === 'string' || typeof value === 'number') {
-    nodes.push({type: 'text', value: String(value)})
-  } else if (typeof value === 'object' && 'length' in value) {
-    while (++index < value.length) {
-      addChild(nodes, value[index])
-    }
-  } else if (typeof value === 'object' && 'type' in value) {
-    if (value.type === 'root') {
-      addChild(nodes, value.children)
-    } else {
-      nodes.push(value)
-    }
-  } else {
-    throw new Error('Expected node, nodes, or string, got `' + value + '`')
-  }
-}
-
-// Parse a single primitives.
-function parsePrimitive(info, name, value) {
-  var result = value
-
-  if ((info.number || info.positiveNumber) && !isNaN(result) && result !== '') {
-    result = Number(result)
-  }
-
-  // Accept `boolean` and `string`.
-  if (
-    (info.boolean || info.overloadedBoolean) &&
-    typeof result === 'string' &&
-    (result === '' || normalize(value) === normalize(name))
-  ) {
-    result = true
-  }
-
-  return result
-}
-
-function style(value) {
-  var result = []
-  var key
-
-  for (key in value) {
-    result.push([key, value[key]].join(': '))
-  }
-
-  return result.join('; ')
-}
-
-function createAdjustMap(values) {
-  var result = {}
-  var index = -1
-
-  while (++index < values.length) {
-    result[values[index].toLowerCase()] = values[index]
-  }
-
-  return result
-}
diff --git a/html.js b/html.js
deleted file mode 100644
index a57c6d0..0000000
--- a/html.js
+++ /dev/null
@@ -1,9 +0,0 @@
-'use strict'
-
-var schema = require('property-information/html')
-var factory = require('./factory')
-
-var html = factory(schema, 'div')
-html.displayName = 'html'
-
-module.exports = html
diff --git a/index.js b/index.js
index 50f2197..79c9d0c 100644
--- a/index.js
+++ b/index.js
@@ -1,3 +1,211 @@
-'use strict'
+import {html, svg, find, normalize} from 'property-information'
+import {parseSelector} from 'hast-util-parse-selector'
+import {parse as spaces} from 'space-separated-tokens'
+import {parse as commas} from 'comma-separated-tokens'
+import {svgCaseSensitiveTagNames} from './svg-case-sensitive-tag-names.js'
 
-module.exports = require('./html')
+var own = {}.hasOwnProperty
+
+export const h = factory(html, 'div')
+h.displayName = 'html'
+
+export const s = factory(svg, 'g', svgCaseSensitiveTagNames)
+s.displayName = 'svg'
+
+function factory(schema, defaultTagName, caseSensitive) {
+  var adjust = caseSensitive && createAdjustMap(caseSensitive)
+
+  return h
+
+  // Hyperscript compatible DSL for creating virtual hast trees.
+  function h(selector, properties) {
+    var node =
+      selector === undefined || selector === null
+        ? {type: 'root', children: []}
+        : parseSelector(selector, defaultTagName)
+    var name =
+      selector === undefined || selector === null
+        ? null
+        : node.tagName.toLowerCase()
+    var index = 1
+    var property
+
+    // Normalize the name.
+    if (name !== undefined && name !== null) {
+      node.tagName = adjust && own.call(adjust, name) ? adjust[name] : name
+    }
+
+    // Handle props.
+    if (properties) {
+      if (
+        name === undefined ||
+        name === null ||
+        typeof properties === 'string' ||
+        'length' in properties ||
+        isNode(name, properties)
+      ) {
+        // Nope, it’s something for `children`.
+        index--
+      } else {
+        for (property in properties) {
+          if (own.call(properties, property)) {
+            addProperty(schema, node.properties, property, properties[property])
+          }
+        }
+      }
+    }
+
+    // Handle children.
+    while (++index < arguments.length) {
+      addChild(node.children, arguments[index])
+    }
+
+    if (name === 'template') {
+      node.content = {type: 'root', children: node.children}
+      node.children = []
+    }
+
+    return node
+  }
+}
+
+function isNode(name, value) {
+  var type = value.type
+
+  if (name === 'input' || !type || typeof type !== 'string') {
+    return false
+  }
+
+  if (typeof value.children === 'object' && 'length' in value.children) {
+    return true
+  }
+
+  type = type.toLowerCase()
+
+  if (name === 'button') {
+    return (
+      type !== 'menu' &&
+      type !== 'submit' &&
+      type !== 'reset' &&
+      type !== 'button'
+    )
+  }
+
+  return 'value' in value
+}
+
+function addProperty(schema, properties, key, value) {
+  var info = find(schema, key)
+  var result = value
+  var index = -1
+  var finalResult
+
+  // Ignore nullish and NaN values.
+  if (
+    result === undefined ||
+    result === null ||
+    (typeof result === 'number' && Number.isNaN(result))
+  ) {
+    return
+  }
+
+  // Handle list values.
+  if (typeof result === 'string') {
+    if (info.spaceSeparated) {
+      result = spaces(result)
+    } else if (info.commaSeparated) {
+      result = commas(result)
+    } else if (info.commaOrSpaceSeparated) {
+      result = spaces(commas(result).join(' '))
+    }
+  }
+
+  // Accept `object` on style.
+  if (info.property === 'style' && typeof result !== 'string') {
+    result = style(result)
+  }
+
+  // Class names (which can be added both on the `selector` and here).
+  if (info.property === 'className' && properties.className) {
+    result = properties.className.concat(result)
+  }
+
+  if (typeof result === 'object' && 'length' in result) {
+    finalResult = []
+    while (++index < result.length) {
+      finalResult[index] = parsePrimitive(info, info.property, result[index])
+    }
+  } else {
+    finalResult = parsePrimitive(info, info.property, result)
+  }
+
+  properties[info.property] = finalResult
+}
+
+function addChild(nodes, value) {
+  var index = -1
+
+  if (typeof value === 'string' || typeof value === 'number') {
+    nodes.push({type: 'text', value: String(value)})
+  } else if (typeof value === 'object' && 'length' in value) {
+    while (++index < value.length) {
+      addChild(nodes, value[index])
+    }
+  } else if (typeof value === 'object' && 'type' in value) {
+    if (value.type === 'root') {
+      addChild(nodes, value.children)
+    } else {
+      nodes.push(value)
+    }
+  } else {
+    throw new Error('Expected node, nodes, or string, got `' + value + '`')
+  }
+}
+
+// Parse a single primitives.
+function parsePrimitive(info, name, value) {
+  var result = value
+
+  if (
+    (info.number || info.positiveNumber) &&
+    !Number.isNaN(Number(result)) &&
+    result !== ''
+  ) {
+    result = Number(result)
+  }
+
+  // Accept `boolean` and `string`.
+  if (
+    (info.boolean || info.overloadedBoolean) &&
+    typeof result === 'string' &&
+    (result === '' || normalize(value) === normalize(name))
+  ) {
+    result = true
+  }
+
+  return result
+}
+
+function style(value) {
+  var result = []
+  var key
+
+  for (key in value) {
+    if (own.call(value, key)) {
+      result.push([key, value[key]].join(': '))
+    }
+  }
+
+  return result.join('; ')
+}
+
+function createAdjustMap(values) {
+  var result = {}
+  var index = -1
+
+  while (++index < values.length) {
+    result[values[index].toLowerCase()] = values[index]
+  }
+
+  return result
+}
diff --git a/package.json b/package.json
index 3ece52f..e33c4d3 100644
--- a/package.json
+++ b/package.json
@@ -27,56 +27,46 @@
   "contributors": [
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "types": "index.d.ts",
   "files": [
     "index.d.ts",
-    "svg.d.ts",
     "index.js",
-    "factory.js",
-    "html.js",
-    "svg.js",
-    "svg-case-sensitive-tag-names.json"
+    "svg-case-sensitive-tag-names.d.ts",
+    "svg-case-sensitive-tag-names.js"
   ],
   "dependencies": {
     "@types/hast": "^2.0.0",
-    "comma-separated-tokens": "^1.0.0",
-    "hast-util-parse-selector": "^2.0.0",
-    "property-information": "^5.0.0",
-    "space-separated-tokens": "^1.0.0"
+    "comma-separated-tokens": "^2.0.0",
+    "hast-util-parse-selector": "^3.0.0",
+    "property-information": "^6.0.0",
+    "space-separated-tokens": "^2.0.0"
   },
   "devDependencies": {
     "@babel/core": "^7.0.0",
     "@babel/plugin-syntax-jsx": "^7.0.0",
     "@babel/plugin-transform-react-jsx": "^7.0.0",
-    "browserify": "^17.0.0",
-    "buble": "^0.20.0",
-    "dtslint": "^4.0.0",
-    "nyc": "^15.0.0",
+    "acorn": "^6.0.0",
+    "acorn-jsx": "^5.0.0",
+    "astring": "^1.0.0",
+    "c8": "^7.0.0",
+    "estree-util-build-jsx": "^2.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
-    "svg-tag-names": "^2.0.0",
+    "svg-tag-names": "^3.0.0",
     "tape": "^5.0.0",
-    "tinyify": "^3.0.0",
-    "unist-builder": "^2.0.0",
-    "xo": "^0.38.0"
+    "unist-builder": "^3.0.0",
+    "xo": "^0.39.0"
   },
   "scripts": {
     "generate": "node script/generate-jsx && node script/build",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
-    "build-bundle": "browserify . -s hastscript > hastscript.js",
-    "build-mangle": "browserify . -s hastscript -p tinyify > hastscript.min.js",
-    "build": "npm run build-bundle && npm run build-mangle",
-    "test-api": "node test",
-    "test-coverage": "nyc --reporter lcov tape test/index.js",
-    "test-types": "dtslint .",
-    "test": "npm run generate && npm run format && npm run build && npm run test-coverage && npm run test-types"
-  },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
+    "test-api": "node test/index.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node test/index.js",
+    "test": "npm run generate && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -88,22 +78,12 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
     "rules": {
-      "eqeqeq": [
-        "error",
-        "always",
-        {
-          "null": "ignore"
-        }
-      ],
-      "guard-for-in": "off",
-      "no-eq-null": "off",
-      "no-self-compare": "off",
-      "unicorn/prefer-number-properties": "off"
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
     },
-    "ignores": [
-      "hastscript.js"
+    "ignore": [
+      "**/*.d.ts"
     ]
   },
   "remarkConfig": {
diff --git a/readme.md b/readme.md
index 044036d..99062bf 100644
--- a/readme.md
+++ b/readme.md
@@ -18,6 +18,9 @@ Use [`unist-builder`][u] to create any [**unist**][unist] tree.
 
 ## Install
 
+This package is [ESM only](https://gist.github.com/sindresorhus/a39789f98801d908bbc7ff3ecc99d99c):
+Node 12+ is needed to use it and it must be `import`ed instead of `require`d.
+
 [npm][]:
 
 ```sh
@@ -27,8 +30,7 @@ npm install hastscript
 ## Use
 
 ```js
-var h = require('hastscript')
-var s = require('hastscript/svg')
+import {h, s} from 'hastscript'
 
 // Children as an array:
 console.log(
@@ -138,6 +140,9 @@ Yields:
 
 ## API
 
+This package exports the following identifiers: `h` and `s`.
+There is no default export.
+
 ### `h(selector?[, properties][, …children])`
 
 ### `s(selector?[, properties][, …children])`
@@ -193,7 +198,7 @@ that SVG can be used too:
 ```jsx
 /** @jsx h */
 /** @jsxFrag null */
-var h = require('hastscript')
+import {h} from 'hastscript'
 
 console.log(
   <div class="foo" id="some-id">
@@ -219,7 +224,7 @@ console.log(
 ```jsx
 /** @jsx s */
 /** @jsxFrag null */
-var s = require('hastscript/svg')
+import {s} from 'hastscript'
 
 console.log(
   <svg xmlns="http://www.w3.org/2000/svg" viewbox="0 0 500 500">
@@ -249,7 +254,7 @@ Babel also lets you configure this in a script:
 ```jsx
 /** @jsx s */
 /** @jsxFrag null */
-var s = require('hastscript/svg')
+import {s} from 'hastscript'
 
 console.log(<rect />)
 ```
diff --git a/script/build.js b/script/build.js
index 928a2ef..a7c2867 100644
--- a/script/build.js
+++ b/script/build.js
@@ -1,12 +1,11 @@
-'use strict'
+import fs from 'fs'
+import {svgTagNames} from 'svg-tag-names'
 
-var fs = require('fs')
-var tagNames = require('svg-tag-names')
+var casing = svgTagNames.filter((d) => d !== d.toLowerCase())
 
-var casing = tagNames.filter(function (d) {
-  return d !== d.toLowerCase()
-})
-
-var doc = JSON.stringify(casing, null, 2) + '\n'
-
-fs.writeFileSync('./svg-case-sensitive-tag-names.json', doc)
+fs.writeFileSync(
+  'svg-case-sensitive-tag-names.js',
+  'export const svgCaseSensitiveTagNames = ' +
+    JSON.stringify(casing, null, 2) +
+    '\n'
+)
diff --git a/script/generate-jsx.js b/script/generate-jsx.js
index a21d6f4..7a379ee 100644
--- a/script/generate-jsx.js
+++ b/script/generate-jsx.js
@@ -1,18 +1,24 @@
-'use strict'
-
-var fs = require('fs')
-var path = require('path')
-var buble = require('buble')
-var babel = require('@babel/core')
+import fs from 'fs'
+import path from 'path'
+import babel from '@babel/core'
+import {Parser} from 'acorn'
+import acornJsx from 'acorn-jsx'
+import {generate} from 'astring'
+import {buildJsx} from 'estree-util-build-jsx'
 
 var doc = String(fs.readFileSync(path.join('test', 'jsx.jsx')))
 
 fs.writeFileSync(
-  path.join('test', 'jsx-buble.js'),
-  buble.transform(doc.replace(/'name'/, "'jsx (buble)'"), {
-    jsx: 'h',
-    jsxFragment: 'null'
-  }).code
+  path.join('test', 'jsx-build-jsx.js'),
+  generate(
+    buildJsx(
+      Parser.extend(acornJsx()).parse(
+        doc.replace(/'name'/, "'jsx (build-jsx)'"),
+        {sourceType: 'module'}
+      ),
+      {pragma: 'h', pragmaFrag: 'null'}
+    )
+  )
 )
 
 fs.writeFileSync(
diff --git a/svg-case-sensitive-tag-names.js b/svg-case-sensitive-tag-names.js
new file mode 100644
index 0000000..575ceef
--- /dev/null
+++ b/svg-case-sensitive-tag-names.js
@@ -0,0 +1,41 @@
+export const svgCaseSensitiveTagNames = [
+  'altGlyph',
+  'altGlyphDef',
+  'altGlyphItem',
+  'animateColor',
+  'animateMotion',
+  'animateTransform',
+  'clipPath',
+  'feBlend',
+  'feColorMatrix',
+  'feComponentTransfer',
+  'feComposite',
+  'feConvolveMatrix',
+  'feDiffuseLighting',
+  'feDisplacementMap',
+  'feDistantLight',
+  'feDropShadow',
+  'feFlood',
+  'feFuncA',
+  'feFuncB',
+  'feFuncG',
+  'feFuncR',
+  'feGaussianBlur',
+  'feImage',
+  'feMerge',
+  'feMergeNode',
+  'feMorphology',
+  'feOffset',
+  'fePointLight',
+  'feSpecularLighting',
+  'feSpotLight',
+  'feTile',
+  'feTurbulence',
+  'foreignObject',
+  'glyphRef',
+  'linearGradient',
+  'radialGradient',
+  'solidColor',
+  'textArea',
+  'textPath'
+]
diff --git a/svg-case-sensitive-tag-names.json b/svg-case-sensitive-tag-names.json
deleted file mode 100644
index 19f0e61..0000000
--- a/svg-case-sensitive-tag-names.json
+++ /dev/null
@@ -1,41 +0,0 @@
-[
-  "altGlyph",
-  "altGlyphDef",
-  "altGlyphItem",
-  "animateColor",
-  "animateMotion",
-  "animateTransform",
-  "clipPath",
-  "feBlend",
-  "feColorMatrix",
-  "feComponentTransfer",
-  "feComposite",
-  "feConvolveMatrix",
-  "feDiffuseLighting",
-  "feDisplacementMap",
-  "feDistantLight",
-  "feDropShadow",
-  "feFlood",
-  "feFuncA",
-  "feFuncB",
-  "feFuncG",
-  "feFuncR",
-  "feGaussianBlur",
-  "feImage",
-  "feMerge",
-  "feMergeNode",
-  "feMorphology",
-  "feOffset",
-  "fePointLight",
-  "feSpecularLighting",
-  "feSpotLight",
-  "feTile",
-  "feTurbulence",
-  "foreignObject",
-  "glyphRef",
-  "linearGradient",
-  "radialGradient",
-  "solidColor",
-  "textArea",
-  "textPath"
-]
diff --git a/svg.d.ts b/svg.d.ts
deleted file mode 100644
index b39440f..0000000
--- a/svg.d.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-// TypeScript Version: 3.5
-
-import hastscript = require('hastscript')
-
-export = hastscript
diff --git a/svg.js b/svg.js
deleted file mode 100644
index b933def..0000000
--- a/svg.js
+++ /dev/null
@@ -1,10 +0,0 @@
-'use strict'
-
-var schema = require('property-information/svg')
-var caseSensitive = require('./svg-case-sensitive-tag-names.json')
-var factory = require('./factory')
-
-var svg = factory(schema, 'g', caseSensitive)
-svg.displayName = 'svg'
-
-module.exports = svg
diff --git a/test/core.js b/test/core.js
index 045c21f..2c395fd 100644
--- a/test/core.js
+++ b/test/core.js
@@ -1,8 +1,5 @@
-'use strict'
-
-var test = require('tape')
-var s = require('../svg')
-var h = require('../html')
+import test from 'tape'
+import {h, s} from '../index.js'
 
 test('hastscript', function (t) {
   t.equal(typeof h, 'function', 'should expose a function')
@@ -476,7 +473,7 @@ test('hastscript', function (t) {
       )
 
       t.deepEqual(
-        h('', {foo: NaN}),
+        h('', {foo: Number.NaN}),
         {
           type: 'element',
           tagName: 'div',
diff --git a/test/index.js b/test/index.js
index d39cad7..6fcc935 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,7 +1,5 @@
-'use strict'
-
 /* eslint-disable import/no-unassigned-import */
-require('./core')
-require('./jsx-babel')
-require('./jsx-buble')
+import './core.js'
+import './jsx-babel.js'
+import './jsx-build-jsx.js'
 /* eslint-enable import/no-unassigned-import */
diff --git a/test/jsx.jsx b/test/jsx.jsx
index 2dc7856..f49af52 100644
--- a/test/jsx.jsx
+++ b/test/jsx.jsx
@@ -1,8 +1,6 @@
-'use strict'
-
-var test = require('tape')
-var u = require('unist-builder')
-var h = require('..')
+import test from 'tape'
+import {u} from 'unist-builder'
+import {h} from '../index.js'
 
 test('name', function (t) {
   t.deepEqual(<a />, h('a'), 'should support a self-closing element')