Add helper methods to extend classes

mod_examples/class_extensions.js

@@ -0,0 +1,32 @@
+/**
+ * Shows how to extend builtin classes
+ */
+
+const METADATA = {
+    website: "https://tobspr.io",
+    author: "tobspr",
+    name: "Mod Example: Class Extensions",
+    version: "1",
+    id: "class-extensions",
+    description: "Shows how to extend builtin classes",
+};
+
+class Mod extends shapez.Mod {
+    init() {
+        this.modInterface.extendClass(shapez.MetaBeltBuilding, {
+            // this replaces a regular method
+            getShowWiresLayerPreview() {
+                return true;
+            },
+
+            // Instead of super, use this.$super()
+            getIsReplaceable() {
+                return this.$super.getIsReplaceable.call(this);
+            },
+
+            getIsRemoveable() {
+                return false;
+            },
+        });
+    }
+}

src/js/mods/mod_interface.js

@@ -388,4 +388,19 @@ export class ModInterface {
             return returnValue;
         };
     }
+
+    extendClass(classHandle, extensionClass) {
+        const extendPrototype = function (base, extension) {
+            const properties = Array.from(Object.getOwnPropertyNames(extension));
+            base.$super = base.$super || {};
+            properties.forEach(propertyName => {
+                if (["constructor", "name", "length", "prototype"].includes(propertyName)) {
+                    return;
+                }
+                base.$super[propertyName] = base.$super[propertyName] || base[propertyName];
+                base[propertyName] = extension[propertyName];
+            });
+        };
+        extendPrototype(classHandle.prototype, extensionClass);
+    }
 }