diff --git a/source/data/extend.mjs b/source/data/extend.mjs
index b97dddf92bc20f3661f93b63684e81f035406dd9..f2febdc19c13705e19870b00deae1bd8b83aa60b 100644
--- a/source/data/extend.mjs
+++ b/source/data/extend.mjs
@@ -5,17 +5,15 @@
  * License text available at https://www.gnu.org/licenses/agpl-3.0.en.html
  */
 
-import { isArray, isObject } from "../types/is.mjs";
-import { typeOf } from "../types/typeof.mjs";
+import {isArray, isObject} from "../types/is.mjs";
+import {typeOf} from "../types/typeof.mjs";
 
-export { extend };
+export {extend};
 
 /**
  * Extend copies all enumerable own properties from one or
  * more source objects to a target object. It returns the modified target object.
  *
- * @param {object} target
- * @param {object}
  * @return {object}
  * @license AGPLv3
  * @since 1.10.0
@@ -24,57 +22,68 @@ export { extend };
  * @throws {Error} unsupported argument
  * @throws {Error} type mismatch
  * @throws {Error} unsupported argument
+ * @param args
  */
 function extend(...args) {
-	let o;
-	let i;
+    let o;
+    let i;
 
-	if (typeof args !== "object" || args[0] === null) {
-		throw new Error(`unsupported argument ${JSON.stringify(args[0])}`);
-	}
+    if (typeof args !== "object" || args[0] === null) {
+        throw new Error(`unsupported argument ${JSON.stringify(args[0])}`);
+    }
 
-	for (i = 0; i < args.length; i++) {
-		const a = args[i];
+    for (i = 0; i < args.length; i++) {
+        const a = args[i];
 
-		if (!(isObject(a) || isArray(a))) {
-			throw new Error(`unsupported argument ${JSON.stringify(a)}`);
-		}
+        if (!(isObject(a) || isArray(a))) {
+            throw new Error(`unsupported argument ${JSON.stringify(a)}`);
+        }
 
-		if (o === undefined) {
-			o = a;
-			continue;
-		}
+        if (o === undefined) {
+            o = a;
+            continue;
+        }
 
-		for (const k in a) {
-			const v = a?.[k];
+        for (const k in a) {
+            const v = a?.[k];
 
-			if (v === o?.[k]) {
-				continue;
-			}
+            if (v === o?.[k]) {
+                continue;
+            }
 
-			if ((isObject(v) && typeOf(v) === "object") || isArray(v)) {
-				if (o[k] === undefined) {
-					if (isArray(v)) {
-						o[k] = [];
-					} else {
-						o[k] = {};
-					}
-				} else {
-					if (typeOf(o[k]) !== typeOf(v)) {
-						throw new Error(
-							`type mismatch: ${JSON.stringify(o[k])}(${typeOf(
-								o[k],
-							)}) != ${JSON.stringify(v)}(${typeOf(v)})`,
-						);
-					}
-				}
+            if ((isObject(v) && typeOf(v) === "object") || isArray(v)) {
+                if (o[k] === undefined) {
+                    if (isArray(v)) {
+                        o[k] = [];
+                    } else {
+                        o[k] = {};
+                    }
+                } else {
+                    if (typeOf(o[k]) !== typeOf(v)) {
+                        throw new Error(
+                            `type mismatch: ${JSON.stringify(o[k])}(${typeOf(
+                                o[k],
+                            )}) != ${JSON.stringify(v)}(${typeOf(v)})`,
+                        );
+                    }
+                }
+                
+                if (isArray(o[k])) {
+                    o[k] = [];
+                    o[k].push(...v);
+                    continue;
+                }
 
-				o[k] = extend(o[k], v);
-			} else {
-				o[k] = v;
-			}
-		}
-	}
+                o[k] = extend(o[k], v);
+            } else {
+                if (isArray(o)) {
+                    o.push(v);
+                    continue;
+                }
+                o[k] = v;
+            }
+        }
+    }
 
-	return o;
+    return o;
 }