iOS devices - HTTP get request response throws error

I'm working with iOS mobile devices (Safari/Chrome) that will throw an error saying the function is undefined when it receives the response. The following is the response from the server:

  "addr": "000",
  "cv1": "4224453",
  "cv2": "Target",

The error does not occur in any other device/browser combo (Android/PC Chrome/Safari). The function is defined before the request is made and should therefore be defined on the page.

I also haven't seen a function being passed as response data before. Is this even common practice?

Please help! Thank you in advance.. (:

FYI: Server is a client's and I cannot change the response data.