add enemy

common/entity.js

@@ -10,13 +10,19 @@ class Entity {
         let ent = this;
         let { width, height } = game;
 
+        let bounced = false;
+
         if (Math.abs(ent.pos.x) >= width / 2) {
             ent.vel.x = (Math.abs(ent.vel.x) + 10) * -Math.sign(ent.pos.x);
+            bounced = true;
         }
 
         if (Math.abs(ent.pos.y) >= height / 2) {
             ent.vel.y = (Math.abs(ent.vel.y) + 10) * -Math.sign(ent.pos.y);
+            bounced = true;
         }
+
+        return bounced;
     }
 }