Use ESM

.gitignore

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

.prettierignore

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

index.js

@@ -1,11 +1,7 @@
-'use strict'
+import events from 'events'
+import once from 'once'
 
-module.exports = stream
-
-var events = require('events')
-var once = require('once')
-
-function stream(processor) {
+export function stream(processor) {
   var chunks = []
   var emitter = new events.EventEmitter()
   var ended
@@ -47,7 +43,7 @@ function stream(processor) {
   // If messages are triggered during the process, those are triggerd as
   // `warning`s.
   function end() {
-    write.apply(null, arguments)
+    write(...arguments)
 
     ended = true
 

package.json

@@ -17,34 +17,31 @@
   "contributors": [
     "Titus Wormer <[email protected]> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "files": [
     "index.js"
   ],
   "dependencies": {
     "once": "^1.4.0"
   },
   "devDependencies": {
+    "c8": "^7.0.0",
     "is-function": "^1.0.0",
-    "nyc": "^15.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "tape": "^5.0.0",
     "unified": "^9.0.0",
-    "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.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node --conditions development test.js",
     "test": "npm run format && npm run test-coverage"
   },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
-  },
   "prettier": {
     "tabWidth": 2,
     "useTabs": false,
@@ -55,8 +52,9 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
     "rules": {
+      "no-var": "off",
+      "prefer-arrow-callback": "off",
       "unicorn/explicit-length-check": "off",
       "unicorn/prefer-reflect-apply": "off"
     }

readme.md

@@ -13,6 +13,9 @@ Note that the interface is streaming, but the code buffers.
 
 ## 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
@@ -33,7 +36,10 @@ process.stdin.pipe(stream(rehype().use(format))).pipe(process.stdout)
 
 ## API
 
-### `createStream(processor)`
+This package exports the following identifiers: `stream`.
+There is no default export.
+
+### `stream(processor)`
 
 Create a readable/writable stream that transforms with `processor`.
 

test.js

@@ -1,16 +1,14 @@
-'use strict'
+import nodeStream from 'stream'
+import test from 'tape'
+import unified from 'unified'
+import func from 'is-function'
+import {stream} from './index.js'
 
-var stream = require('stream')
-var test = require('tape')
-var unified = require('unified')
-var func = require('is-function')
-var createStream = require('.')
-
-test('createStream', function (t) {
+test('stream', function (t) {
   var proc = unified().use(parse).use(stringify)
 
   t.test('interface', function (st) {
-    var tr = createStream(proc)
+    var tr = stream(proc)
     st.equal(tr.readable, true, 'should be readable')
     st.equal(tr.writable, true, 'should be writable')
     st.ok(func(tr.write), 'should have a `write` method')
@@ -25,39 +23,39 @@ test('createStream', function (t) {
 
     st.plan(10)
 
-    st.equal(createStream(proc).end(), true, 'should return true')
+    st.equal(stream(proc).end(), true, 'should return true')
 
     st.throws(
       function () {
-        var tr = createStream(proc)
+        var tr = stream(proc)
         tr.end()
         tr.end()
       },
       /^Error: Did not expect `write` after `end`$/,
       'should throw on end after end'
     )
 
-    createStream(proc)
+    stream(proc)
       .on('data', function (value) {
         st.equal(value, '', 'should emit processed `data`')
       })
       .end()
 
-    createStream(proc)
+    stream(proc)
       .on('data', function (value) {
         st.equal(value, 'alpha', 'should emit given `data`')
       })
       .end('alpha')
 
-    createStream(proc)
+    stream(proc)
       .on('data', function (value) {
         st.equal(value, 'brC!vo', 'should honour encoding')
       })
       .end(Buffer.from([0x62, 0x72, 0xc3, 0xa1, 0x76, 0x6f]), 'ascii')
 
     phase = 0
 
-    createStream(proc)
+    stream(proc)
       .on('data', function () {
         st.equal(phase, 1, 'should trigger data after callback')
         phase++
@@ -69,7 +67,7 @@ test('createStream', function (t) {
 
     exception = new Error('alpha')
 
-    createStream(
+    stream(
       proc().use(function () {
         return transformer
         function transformer() {
@@ -89,7 +87,7 @@ test('createStream', function (t) {
       )
       .end()
 
-    createStream(
+    stream(
       proc().use(function () {
         return transformer
         function transformer(tree, file) {
@@ -118,13 +116,13 @@ test('createStream', function (t) {
 
     st.doesNotThrow(function () {
       // Not writable.
-      var tr = createStream(proc)
-      tr.pipe(new stream.Readable())
+      var tr = stream(proc)
+      tr.pipe(new nodeStream.Readable())
       tr.end('foo')
     }, 'should not throw when piping to a non-writable stream')
 
-    tr = createStream(proc)
-    s = new stream.PassThrough()
+    tr = stream(proc)
+    s = new nodeStream.PassThrough()
     s._isStdio = true
 
     tr.pipe(s)
@@ -137,15 +135,15 @@ test('createStream', function (t) {
       s.write('delta')
     }, 'should not `end` stdio streams')
 
-    tr = createStream(proc).on('error', function (error) {
+    tr = stream(proc).on('error', function (error) {
       st.equal(error.message, 'Whoops!', 'should pass errors')
     })
 
-    tr.pipe(new stream.PassThrough())
+    tr.pipe(new nodeStream.PassThrough())
     tr.emit('error', new Error('Whoops!'))
 
-    tr = createStream(proc)
-    tr.pipe(new stream.PassThrough())
+    tr = stream(proc)
+    tr.pipe(new nodeStream.PassThrough())
 
     st.throws(
       function () {
@@ -155,9 +153,9 @@ test('createStream', function (t) {
       'should throw if errors are not listened to'
     )
 
-    tr = createStream(proc)
+    tr = stream(proc)
 
-    tr.pipe(new stream.PassThrough())
+    tr.pipe(new nodeStream.PassThrough())
       .on('data', function (buf) {
         st.equal(
           String(buf),