The Verj.io Ajax mechanism processes Client-Server API call at a time. If the Ajax mechanism is called it will ignore any another request until the original request has completed.
Multiple Client-Server API calls can be chained together by using the executeFunctionAsynchronously() function and calling the next Client-Server API function from inside either the successCallback or failureCallback function as appropriate. However, where possible, you should avoid making any simultaneous Client-Server API calls.