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

@@ -1,12 +1,6 @@
-'use strict'
-
-var WeakMap = require('es6-weak-map')
-
 var cache = new WeakMap()
 
-module.exports = parents
-
-function parents(ast) {
+export function parents(ast) {
   return wrapNode(ast, null)
 }
 

package.json

@@ -27,15 +27,15 @@
     "Eugene Sharygin <eush77@gmail.com>",
     "Titus Wormer <tituswormer@gmail.com> (https://wooorm.com)"
   ],
+  "sideEffects": false,
+  "type": "module",
+  "main": "index.js",
   "files": [
     "index.js"
   ],
-  "dependencies": {
-    "es6-weak-map": "^2.0.0"
-  },
   "devDependencies": {
+    "c8": "^7.0.0",
     "clone": "^2.0.0",
-    "nyc": "^15.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
@@ -44,16 +44,10 @@
   },
   "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 test.js",
+    "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node 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,
@@ -64,10 +58,9 @@
   },
   "xo": {
     "prettier": true,
-    "esnext": false,
     "rules": {
-      "unicorn/no-reduce": "off",
-      "unicorn/no-fn-reference-in-iterator": "off"
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
     }
   },
   "remarkConfig": {

readme.md

@@ -19,6 +19,9 @@ which it originated.
 
 ## 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
@@ -28,8 +31,8 @@ npm install unist-util-parents
 ## Use
 
 ```js
-var u = require('unist-builder')
-var parents = require('unist-util-parents')
+import {u} from 'unist-builder'
+import {parents} from 'unist-util-parents'
 
 var tree = u('root', [
   u('leaf', 'leaf 1'),
@@ -62,11 +65,14 @@ console.log(chain)
 Yields:
 
 ```js
-[ 'root', 'node', 'node', 'node', 'leaf' ]
+['root', 'node', 'node', 'node', 'leaf']
 ```
 
 ## API
 
+This package exports the following identifiers: `parents`.
+There is no default export.
+
 ### `parents(tree)`
 
 Returns a wrapped `tree` with a proxy that imposes two additional properties on

test.js

@@ -1,8 +1,6 @@
-'use strict'
-
-var test = require('tape')
-var clone = require('clone')
-var parents = require('.')
+import test from 'tape'
+import clone from 'clone'
+import {parents} from './index.js'
 
 var ast = {
   type: 'root',