Breaking: 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

@@ -1,7 +1,19 @@
 {
     "extends": "eslint",
     "env": {
-        "es6": true,
-        "node": true
-    }
+        "es2020": true
+    },
+    "parserOptions": {
+        "sourceType": "module",
+        "ecmaVersion": 2020
+    },
+    "overrides": [
+        {
+            "files": ["*.cjs"],
+            "parserOptions": {
+                "sourceType": "script"
+            }
+        }
+    ],
+    "ignorePatterns": ["/dist", "/coverage"]
 }

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        node: [14.x, 12.x, 10.x]
+        node: [16.x, 14.x, 12.x, "12.22.0"]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: actions/checkout@v2

.gitignore

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

README.md

@@ -21,6 +21,14 @@ $ npm install eslint-visitor-keys
 
 ## 📖 Usage
 
+To use in an ESM file:
+
+```js
+import * as evk from "eslint-visitor-keys"
+```
+
+To use in a CommonJS file:
+
 ```js
 const evk = require("eslint-visitor-keys")
 ```

lib/index.js

@@ -2,18 +2,7 @@
  * @author Toru Nagashima <https://github.com/mysticatea>
  * See LICENSE file in root directory for full license.
  */
-"use strict";
-
-const KEYS = require("./visitor-keys.json");
-
-// Types.
-const NODE_TYPES = Object.freeze(Object.keys(KEYS));
-
-// Freeze the keys.
-for (const type of NODE_TYPES) {
-    Object.freeze(KEYS[type]);
-}
-Object.freeze(KEYS);
+import KEYS from "./visitor-keys.js";
 
 // List to ignore keys.
 const KEY_BLACKLIST = new Set([
@@ -31,51 +20,40 @@ function filterKey(key) {
     return !KEY_BLACKLIST.has(key) && key[0] !== "_";
 }
 
-//------------------------------------------------------------------------------
-// Public interfaces
-//------------------------------------------------------------------------------
-
-module.exports = Object.freeze({
-
-    /**
-     * Visitor keys.
-     * @type {{ [type: string]: string[] | undefined }}
-     */
-    KEYS,
-
-    /**
-     * Get visitor keys of a given node.
-     * @param {Object} node The AST node to get keys.
-     * @returns {string[]} Visitor keys of the node.
-     */
-    getKeys(node) {
-        return Object.keys(node).filter(filterKey);
-    },
-
-    // Disable valid-jsdoc rule because it reports syntax error on the type of @returns.
-    // eslint-disable-next-line valid-jsdoc
-    /**
-     * Make the union set with `KEYS` and given keys.
-     * @param {Object} additionalKeys The additional keys.
-     * @returns {{ [type: string]: string[] | undefined }} The union set.
-     */
-    unionWith(additionalKeys) {
-        const retv = Object.assign({}, KEYS);
+/**
+ * Get visitor keys of a given node.
+ * @param {Object} node The AST node to get keys.
+ * @returns {string[]} Visitor keys of the node.
+ */
+export function getKeys(node) {
+    return Object.keys(node).filter(filterKey);
+}
 
-        for (const type of Object.keys(additionalKeys)) {
-            if (retv.hasOwnProperty(type)) {
-                const keys = new Set(additionalKeys[type]);
+// Disable valid-jsdoc rule because it reports syntax error on the type of @returns.
+// eslint-disable-next-line valid-jsdoc
+/**
+ * Make the union set with `KEYS` and given keys.
+ * @param {Object} additionalKeys The additional keys.
+ * @returns {{ [type: string]: string[] | undefined }} The union set.
+ */
+export function unionWith(additionalKeys) {
+    const retv = Object.assign({}, KEYS);
 
-                for (const key of retv[type]) {
-                    keys.add(key);
-                }
+    for (const type of Object.keys(additionalKeys)) {
+        if (Object.prototype.hasOwnProperty.call(retv, type)) {
+            const keys = new Set(additionalKeys[type]);
 
-                retv[type] = Object.freeze(Array.from(keys));
-            } else {
-                retv[type] = Object.freeze(Array.from(additionalKeys[type]));
+            for (const key of retv[type]) {
+                keys.add(key);
             }
-        }
 
-        return Object.freeze(retv);
+            retv[type] = Object.freeze(Array.from(keys));
+        } else {
+            retv[type] = Object.freeze(Array.from(additionalKeys[type]));
+        }
     }
-});
+
+    return Object.freeze(retv);
+}
+
+export { KEYS };