SplashScreen/custom animation when resource loading

Hello!
When I start my game on browsers, there is black screen for a while when resources are loading. I know how to do it with Cocos2d-html5, but how to create splashscreen custom image/animation at start or how to manually define when resources are loaded? I want to play simple animation and in the same time load all resources in background. Is that possible with CocosBuilder and JSB? If yes, then how? Are CocosBuilder and JSB support this?