Cocos2d js 3.3 relies on RAF (requestAnimationFrame) for animation loop. This function is very gentle with animation, consumes the least resources possible, but the drawback (or super feature, depending how you see it) is that when switching a tab, the RAF does not fire.
If you want to have your game running while in other tabs, like a RTS or multiplayer game that needs to be connected continuously, you must switch to seTimeout/setInterval loop control instead. Don’t know whether the engine has a flag for this (the WIP V4 does), but it is the only way.
Hope that helps.