New: Switch to ESM

.editorconfig

@@ -0,0 +1,15 @@
+; EditorConfig file: https://EditorConfig.org
+; Install the "EditorConfig" plugin into your editor to use
+
+root = true
+
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+indent_style = space
+indent_size = 4
+trim_trailing_whitespace = true
+
+[package.json]
+indent_size = 2

.eslintrc.json

@@ -1,5 +1,9 @@
 {
     "extends": "eslint",
+    "parserOptions": {
+        "sourceType": "module",
+        "ecmaVersion": "2020"
+    },
     "env": {
         "es6": true,
         "node": true

.gitignore

@@ -4,3 +4,4 @@
 /node_modules
 /test.*
 .eslint-release-info.json
+/dist

README.md

@@ -22,7 +22,7 @@ $ npm install eslint-visitor-keys
 ## 📖 Usage
 
 ```js
-const evk = require("eslint-visitor-keys")
+import evk from "eslint-visitor-keys"
 ```
 
 ### evk.KEYS

lib/index.js

@@ -2,9 +2,11 @@
  * @author Toru Nagashima <https://github.com/mysticatea>
  * See LICENSE file in root directory for full license.
  */
-"use strict";
+import { readFileSync } from "fs";
 
-const KEYS = require("./visitor-keys.json");
+const KEYS = JSON.parse(
+    readFileSync(new URL("./visitor-keys.json", import.meta.url))
+);
 
 // Types.
 const NODE_TYPES = Object.freeze(Object.keys(KEYS));
@@ -35,7 +37,7 @@ function filterKey(key) {
 // Public interfaces
 //------------------------------------------------------------------------------
 
-module.exports = Object.freeze({
+export default Object.freeze({
 
     /**
      * Visitor keys.
@@ -63,7 +65,7 @@ module.exports = Object.freeze({
         const retv = Object.assign({}, KEYS);
 
         for (const type of Object.keys(additionalKeys)) {
-            if (retv.hasOwnProperty(type)) {
+            if (Object.prototype.hasOwnProperty.call(retv, type)) {
                 const keys = new Set(additionalKeys[type]);
 
                 for (const key of retv[type]) {

package.json

@@ -2,25 +2,33 @@
   "name": "eslint-visitor-keys",
   "version": "2.1.0",
   "description": "Constants and utilities about visitor keys to traverse AST.",
+  "type": "module",
   "main": "lib/index.js",
+  "exports": {
+    "import": "./lib/index.js",
+    "require": "./dist/eslint-visitor-keys.cjs"
+  },
   "files": [
     "lib"
   ],
   "engines": {
-    "node": ">=10"
+    "node": ">=12"
   },
   "devDependencies": {
-    "eslint": "^4.7.2",
-    "eslint-config-eslint": "^4.0.0",
+    "c8": "^7.7.3",
+    "eslint": "^7.29.0",
+    "eslint-config-eslint": "^7.0.0",
     "eslint-release": "^3.1.2",
-    "mocha": "^3.5.3",
-    "nyc": "^11.2.1",
-    "opener": "^1.4.3"
+    "mocha": "^9.0.1",
+    "opener": "^1.5.2",
+    "rollup": "^2.52.1"
   },
   "scripts": {
+    "prepare": "npm run build",
+    "build": "rollup -c",
     "lint": "eslint lib tests/lib",
-    "test": "nyc mocha tests/lib",
-    "coverage": "nyc report --reporter lcov && opener coverage/lcov-report/index.html",
+    "test": "c8 mocha tests/lib",
+    "coverage": "c8 report --reporter lcov && opener coverage/lcov-report/index.html",
     "generate-release": "eslint-generate-release",
     "generate-alpharelease": "eslint-generate-prerelease alpha",
     "generate-betarelease": "eslint-generate-prerelease beta",

rollup.config.js

@@ -0,0 +1,9 @@
+export default {
+    input: "./lib/index.js",
+    external: ["fs"],
+    output: {
+        exports: "default",
+        format: "cjs",
+        file: "dist/eslint-visitor-keys.cjs"
+    }
+};

tests/lib/index.js

@@ -2,11 +2,9 @@
  * @author Toru Nagashima <https://github.com/mysticatea>
  * See LICENSE file in root directory for full license.
  */
-"use strict";
-
-const assert = require("assert");
-const fs = require("fs");
-const evk = require("../..");
+import assert from "assert";
+import fs from "fs";
+import evk from "../../lib/index.js";
 
 const keys = JSON.parse(fs.readFileSync("lib/visitor-keys.json", "utf8"));