Update class extensions

mod_examples/class_extensions.js

@@ -8,22 +8,24 @@ const METADATA = {
     description: "Shows how to extend builtin classes",
 };
 
-class Mod extends shapez.Mod {
-    init() {
-        this.modInterface.extendClass(shapez.MetaBeltBuilding, {
-            // this replaces a regular method
+const BeltExtension = ({ $super, $old }) => ({
     getShowWiresLayerPreview() {
-                return true;
+        // Access the old method
+        return !$old.getShowWiresLayerPreview();
     },
 
-            // Instead of super, use this.$super()
     getIsReplaceable() {
-                return this.$super.getIsReplaceable.call(this);
+        // Instead of super, use $super
+        return $super.getIsReplaceable.call(this);
     },
 
     getIsRemoveable() {
         return false;
     },
-        });
+});
+
+class Mod extends shapez.Mod {
+    init() {
+        this.modInterface.extendClass(shapez.MetaBeltBuilding, BeltExtension);
     }
 }

src/js/mods/mod_interface.js

@@ -389,18 +389,24 @@ export class ModInterface {
         };
     }
 
-    extendClass(classHandle, extensionClass) {
-        const extendPrototype = function (base, extension) {
-            const properties = Array.from(Object.getOwnPropertyNames(extension));
-            base.$super = base.$super || {};
+    /**
+     *
+     * @param {typeof Object} classHandle
+     * @param {({ $super, $old }) => any} extender
+     */
+    extendClass(classHandle, extender) {
+        const prototype = classHandle.prototype;
+
+        const $super = Object.getPrototypeOf(prototype);
+        const $old = {};
+        const extensionMethods = extender({ $super, $old });
+        const properties = Array.from(Object.getOwnPropertyNames(extensionMethods));
         properties.forEach(propertyName => {
-                if (["constructor", "name", "length", "prototype"].includes(propertyName)) {
+            if (["constructor", "prototype"].includes(propertyName)) {
                 return;
             }
-                base.$super[propertyName] = base.$super[propertyName] || base[propertyName];
-                base[propertyName] = extension[propertyName];
+            $old[propertyName] = prototype[propertyName];
+            prototype[propertyName] = extensionMethods[propertyName];
         });
-        };
-        extendPrototype(classHandle.prototype, extensionClass);
     }
 }