I'm a beginning learner of webgl. and renctly there is some problems I can't understand. I created the createScene() function and imported some meshes from one .babylon file. When I want to change some materials' diffuse color or some mesh's position and so on, I try the getMaterialByName() or getMeshByName(), the codes just like mat = scene.getMaterialByName(''abc''); but it does not work, my browser display nothing. If I delete the code above, it turns OK. Anyone could tell me why?