diff --git a/main.js b/main.js
index d1b762f..1c7ed6e 100644
--- a/main.js
+++ b/main.js
@@ -1,10 +1,14 @@
 function merge(dst, src) {
     for (let key in src) {
         if (!src.hasOwnProperty(key)) continue;
-        if (dst.hasOwnProperty(key) && isObject(dst[key])) {
+        if (hasOwn(dst, key) && isObject(dst[key])) {
             merge(dst[key], src[key]);
         } else {
             dst[key] = src[key];
         }
     }
 }
+
+function hasOwn(obj, key) {
+    return obj.hasOwnProperty(key)
+}