Use ESM

.gitignore

@@ -1,6 +1,5 @@
 .DS_Store
 *.log
-.nyc_output/
 coverage/
 node_modules/
 yarn.lock

.prettierignore

@@ -1,3 +1,2 @@
 coverage/
-*.json
 *.md

index.js

@@ -1 +1,2 @@
-module.exports = require('./lib/syntax.js')
+export {frontmatterHtml} from './lib/html.js'
+export {frontmatter} from './lib/syntax.js'

lib/html.js

@@ -1,22 +1,19 @@
-module.exports = create
+import {matters} from './matters.js'
 
-var matters = require('./matters.js')
-
-function create(options) {
+export function frontmatterHtml(options) {
   var settings = matters(options)
-  var length = settings.length
   var index = -1
-  var matter
   var enter = {}
   var exit = {}
+  var type
 
-  while (++index < length) {
-    matter = settings[index]
-    enter[matter.type] = start
-    exit[matter.type] = end
+  while (++index < settings.length) {
+    type = settings[index].type
+    enter[type] = start
+    exit[type] = end
   }
 
-  return {enter: enter, exit: exit}
+  return {enter, exit}
 
   function start() {
     this.buffer()

lib/matters.js

@@ -1,12 +1,10 @@
-module.exports = matters
-
-var fault = require('fault')
+import {fault} from 'fault'
 
 var own = {}.hasOwnProperty
 
 var markers = {yaml: '-', toml: '+'}
 
-function matters(options = 'yaml') {
+export function matters(options = 'yaml') {
   var results = []
   var index = -1
 

lib/syntax.js

@@ -1,8 +1,6 @@
-module.exports = create
+import {matters} from './matters.js'
 
-var matters = require('./matters.js')
-
-function create(options) {
+export function frontmatter(options) {
   var settings = matters(options)
   var length = settings.length
   var index = -1
@@ -20,7 +18,7 @@ function create(options) {
     }
   }
 
-  return {flow: flow}
+  return {flow}
 }
 
 function parse(matter) {

package.json

@@ -23,35 +23,31 @@
   "contributors": [
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "files": [
     "lib/",
-    "index.js",
-    "html.js"
+    "index.js"
   ],
   "dependencies": {
-    "fault": "^1.0.0"
+    "fault": "^2.0.0"
   },
   "devDependencies": {
-    "micromark": "~2.11.0",
-    "nyc": "^15.0.0",
+    "c8": "^7.0.0",
+    "micromark": "^3.0.0-alpha.2",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "tape": "^5.0.0",
-    "xo": "^0.38.0"
+    "xo": "^0.39.0"
   },
   "scripts": {
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
-    "test-api": "node test",
-    "test-coverage": "nyc --reporter lcov tape test.js",
+    "test-api": "node --conditions development test/index.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node --conditions development test/index.js",
     "test": "npm run format && npm run test-coverage"
   },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
-  },
   "prettier": {
     "tabWidth": 2,
     "useTabs": false,
@@ -62,8 +58,9 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
     "rules": {
+      "no-var": "off",
+      "prefer-arrow-callback": "off",
       "unicorn/no-this-assignment": "off"
     }
   },

readme.md

@@ -25,6 +25,9 @@ You probably shouldn’t use this package directly, but instead use
 
 ## 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
@@ -33,9 +36,13 @@ npm install micromark-extension-frontmatter
 
 ## API
 
-### `html(options)`
+This package exports the following identifiers: `frontmatter`,
+`frontmatterHtml`.
+There is no default export.
+
+### `frontmatterHtml(options?)`
 
-### `syntax(options)`
+### `frontmatter(options?)`
 
 > Note: `syntax` is the default export of this module, `html` is available at
 > `micromark-extension-frontmatter/html`.

test.js → test/index.js

@@ -1,7 +1,6 @@
-var test = require('tape')
-var micromark = require('micromark')
-var syntax = require('./index.js')
-var html = require('./html.js')
+import test from 'tape'
+import {micromark} from 'micromark'
+import {frontmatter as syntax, frontmatterHtml as html} from '../index.js'
 
 var custom = {type: 'custom', marker: {open: '<', close: '>'}}
 var json = {type: 'json', fence: {open: '{', close: '}'}}