Remove extend dependency, becoming a zero-dependency package

index.js

@@ -1,7 +1,6 @@
 'use strict';
 const fs = require('fs');
 const path = require('path');
-const extend = require('extend');
 
 function load() {
   // Recursively load one or more directories passed as arguments.
@@ -23,7 +22,7 @@ function load() {
 
     // The JSON data is independent of the actual file
     // hierarchy, so it is essential to extend "deeply".
-    result = extend(true, result, extra);
+    extend(result, extra);
   }
 
   for (dir of arguments) {
@@ -34,6 +33,26 @@ function load() {
   return result;
 }
 
+function isPlainObject(v) {
+  return typeof v === 'object' && v !== null && !Array.isArray(v);
+}
+
+function extend(target, source) {
+  if (!isPlainObject(target) || !isPlainObject(source)) {
+    throw new Error('Both target and source must be plain objects');
+  }
+
+  // iterate over own enumerable properties
+  for (const [key, value] of Object.entries(source)) {
+    // recursively extend if target has the same key, otherwise just assign
+    if (Object.prototype.hasOwnProperty.call(target, key)) {
+      extend(target[key], value);
+    } else {
+      target[key] = value;
+    }
+  }
+}
+
 module.exports = load(
   'api',
   'browsers',

package.json

@@ -4,9 +4,6 @@
   "description": "Browser compatibility data provided by MDN Web Docs",
   "main": "index.js",
   "types": "index.d.ts",
-  "dependencies": {
-    "extend": "3.0.2"
-  },
   "engines": {
     "node": ">=10.0.0"
   },