I always go with a design where objects handle themselves (that's what methods are for, after all) but the base World has a list of all the objects that it uses to coordinate them. So something like:

class World { var entities = []; function update() { for each (entity in entities) { entity.update(entities); } } } class Entity { function update(entities) { this.move(); for each (entity in entities) { this.collide(entity); } } } 

I usually go with a design where objects handle themselves (that's what methods are for, after all) but the base World has lists of all the objects and it uses those lists to coordinate them. So something like:

class World { var walls = [];  var actors = [];  function update() { for each (actor in actors) { actor.update(walls); } } } class Actor { function update(walls) { this.move(); for each (wall in walls) { this.collide(wall); } } }