Dart catch clause

Question

I recently stumbled across the following Dart code:

void doSomething(String url, String method) {     HttpRequest request = new HttpRequest();      request.open(method, url);     request.onLoad.listen((event) {         if(request.status < 400) {             try {                 String json = request.responseText;             } catch(e) {                 print("Error!");             }         } else {             print("Error! (400+)");         }     });      request.setRequestHeader("Accept", ApplicationJSON); } 

I'm wondering what the e variable is in the catch clause:

catch(e) {     ... } 

Obviously its some sort of exception, but (1) why do we not need to specify its type, and (2) what could I add in there to specify its concrete type? For instance, how could I handle multiple types of possible exceptions in a similar way to catchError(someHandler, test: (e) => e is SomeException)?

Answer 1

1. Dart is an optional typed language. So the type of e is not required.

2. you have to use the following syntax to catch only SomeException :

try {   // ... } on SomeException catch(e) {  //Handle exception of type SomeException } catch(e) {  //Handle all other exceptions } 

See catch section of Dart: Up and Running.

Finally catch can accept 2 parameters ( catch(e, s) ) where the second parameter is the StackTrace.