Use ESM

Author: wooorm

.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

@@ -1,15 +1,11 @@
-'use strict'
-
-var Map = require('es6-map')
-var visit = require('unist-util-visit')
-
-module.exports = Index
+import Map from 'es6-map'
+import {visit} from 'unist-util-visit'
 
 Index.prototype.get = get
 Index.prototype.add = add
 Index.prototype.remove = remove
 
-function Index(tree, filter, prop) {
+export function Index(tree, filter, prop) {
   var self
 
   if (!(this instanceof Index)) {

package.json

@@ -32,35 +32,32 @@
     "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-map": "^0.1.0",
-    "unist-util-visit": "^2.0.0"
+    "unist-util-visit": "^3.0.0"
   },
   "devDependencies": {
-    "nyc": "^15.0.0",
+    "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
     "tape": "^5.0.0",
-    "unist-builder": "^2.0.0",
-    "unist-util-select": "^3.0.0",
+    "unist-builder": "^3.0.0",
+    "unist-util-select": "^4.0.0",
     "xo": "^0.38.0"
   },
   "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 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,
@@ -73,9 +70,10 @@
     "prettier": true,
     "rules": {
       "unicorn/no-this-assignment": "off",
-      "unicorn/prefer-includes": "off"
-    },
-    "esnext": false
+      "unicorn/prefer-includes": "off",
+      "no-var": "off",
+      "prefer-arrow-callback": "off"
+    }
   },
   "remarkConfig": {
     "plugins": [

readme.md

@@ -13,6 +13,9 @@ computed keys back to nodes.
 
 ## 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
@@ -50,7 +53,10 @@ Yields:
 
 ## API
 
-### `Index([tree[, test], ]prop|keyFn)`
+This package exports the following identifiers: `Index`.
+There is no default export.
+
+### `class Index([tree[, test], ]prop|keyFn)`
 
 Create an index data structure that maps keys (calculated by `keyFn` function or
 the values at `prop` in each node) to a list of nodes.
@@ -60,9 +66,9 @@ by `test`.
 
 ###### Signatures
 
-*   `Index(prop|keyFn)`
-*   `Index(tree, prop|keyFn)`
-*   `Index(tree, test, prop|keyFn)`
+*   `new Index(prop|keyFn)`
+*   `new Index(tree, prop|keyFn)`
+*   `new Index(tree, test, prop|keyFn)`
 
 ###### Parameters
 

test.js

@@ -1,9 +1,7 @@
-'use strict'
-
-var test = require('tape')
-var u = require('unist-builder')
-var select = require('unist-util-select').select
-var Index = require('.')
+import test from 'tape'
+import {u} from 'unist-builder'
+import {select} from 'unist-util-select'
+import {Index} from './index.js'
 
 var index = Index