Hm, but what about some init loading?
I need load some data BEFORE my widget start. In this case i use "sync" calls now. Is it incorrect?
You will need to find some way around using sync calls. We require data for our widget as well, so we call it during the "onApplicationStartup" event. This gets called before the snippet is even fully loaded, which should give you plenty of time to make the request and receive the response. I have never seen an instance where the data was not received by the time I launch into sidebar mode. If the data is not there, you could put up a wait overlay until it is available, or put up some other indication that data is not currently available.
Sync calls are not good in this environment as they block everything else from executing as Javascript is essentially a single threaded environment. If the sync call never completes, then you have a GUI that is frozen, and the user can't do a thing about it.