How to view the front end or back-end bug belonging

How to view the next 1.F12 bug belonging to the front or back end?
Separate front and rear ends of the project, the data request to the backend via ajax, if the rear end of the data returned in question, then the problem is that candidates, if the returned data is no problem, but the results show an abnormal problem usually at the front end.

2. When problems arise app, how to determine the client's problem or the problem of the interface, or server problem?
First determine whether the server interfaces with packet capture tool returns the correct data, so you can rule out the question of whether the server if the server returns an error then that is the reason the server, if the returned data and interface documentation does not match then the problem is the interface, the last is client issues.