I want to ask how to handle some exception in middle of the process (I'm working with PHP).

my js is :

2. $(function(){
3. var request;
4. $('.naviref').on('click',function(){
5. if(request){request.abort();}
6. request = $.ajax({
7. url: "html.php",
8.        type: "post"
9.     });
10. 
    
11. request.done(function (response, textStatus, jqXHR){
12. alert(response);
13.         var text = JSON.parse(response);
14.         alert(text);
15.         if(text.error){
16.         alert(1);}
17. });
18. 
    
19. request.fail(function (jqXHR, textStatus, errorThrown){
20. alert('Error while making the request!');
22. });
23. 
    
24. event.preventDefault();
25. });
26. });

while in the php, the scenario is response the exception in the middle of the process :

2. try{
3. $a=20;
4. $a=21;
5. echo "the first letter : $a <br/>";
6. throw new Exception("This is ERROR",0);
7. echo "the second letter : $b <br/>";
8. }
9. catch(Exception $e){
10. echo json_encode(array(
11. 'error' => array(
12. 'msg' => $e->getMessage()
13. ),
14. ));
15. }

while test this code, alert output is 

the first letter : 21 <br/>{"error":{"msg":"This is ERROR"}}

is there possible to check if there is an error in jquery and parse to another page (exception information page) ?