Bind callbacks to object

src/engine/builders/item.js

@@ -31,12 +31,12 @@ export default class ItemBuilder {
     }
 
     withUseCallback(callback) {
-        this.item.useCallback = callback;
+        this.item.addUseCallback(callback);
         return this;
     }
 
     withTakeCallback(callback) {
-        this.item.takeCallback = callback;
+        this.item.addTakeCallback(callback);
         return this;
     }
 

src/engine/item.js

@@ -17,4 +17,12 @@ export default class Item {
     async onTake() {
         if (this.takeCallback) return this.takeCallback();
     }
+
+    addUseCallback(callback) {
+        this.useCallback = callback.bind(this);
+    }
+
+    addTakeCallback(callback) {
+        this.takeCallback = callback.bind(this);
+    }
 }

src/engine/room.js

@@ -50,23 +50,23 @@ export default class Room {
     }
 
     addEnterCallback(callback) {
-        this.enterCallback = callback;
+        this.enterCallback = callback.bind(this);
     }
 
     addExitCallback(callback) {
-        this.exitCallback = callback;
+        this.exitCallback = callback.bind(this);
     }
 
     addEnterLogic(func) {
-        this.canEnterLogic = func;
+        this.canEnterLogic = func.bind(this);
     }
 
     addExitLogic(func) {
-        this.canExitLogic = func;
+        this.canExitLogic = func.bind(this);
     }
 
     addTickCallback(callback) {
-        this.tickCallback = callback;
+        this.tickCallback = callback.bind(this);
     }
 
     getItems() {