I noticed that when an error is thrown in a try/catch block within a Google Apps Script, Logger.log(e instanceof Error) returns true. But, when that same object is passed back to the client in the catch statement, it logs false.
GAS sample
function isValid() {
return false
}
function testing() {
try {
if(!isValid()) { throw new Error("failure") }
return "success"
} catch(e) {
Logger.log(e instanceof Error) // true
return e // false in the client when tested with console.log(e instanceof Error)
}
}
client
function foo() {
google.script.run.withSuccessHandler(onSuccess).withFailureHandler(onFailure).testing();
}
function onSuccess(e) {
console.log(e instanceof Error) // false
console.log(e) // null
}
function onFailure(e) {
console.log(e instanceof Error) // no result
}
Is there a better way to test for an error returned from the script file?
From the client side, you use a .withFailureHandler(...) when calling the .run.myFunction() code. The failure handler is a function in your client side code that will be called if an exception (i.e. error) is thrown in your server-side code and not handled.
Failure handlers will only be called if an exception is thrown. Otherwise, the success handler receives the server-side function's return value.
.gs
function myFn() {
try {
throw new Error("failure");
}
catch (e) {
Logger.log(e);
// Must rethrow to activate the client's FailureHandler function.
throw e;
}
return "success"
}
.html
function foo() {
google.script.run.withFailureHandler(logError).withSuccessHandler(useReturnValue).myFn();
}
function logError(error) {
console.log(error);
}
function useReturnValue(value) {
// do stuff
}
In the client side console, you will see the error get logged.
The problem is that your e variable hasn't an object assigned. Please note that the official Guides use error as the error handling function argument but your code use data and instead of using it on the console statement you use e.
On your client-side code replace data by e or vice versa.
From https://developers.google.com/apps-script/guides/html/reference/run#withFailureHandler(Function)
Code.gs
function doGet() {
return HtmlService.createHtmlOutputFromFile('Index');
}
function getUnreadEmails() {
// 'got' instead of 'get' will throw an error.
return GmailApp.gotInboxUnreadCount();
}
index.html
<!DOCTYPE html>
<html>
<head>
<base target="_top">
<script>
function onFailure(error) {
var div = document.getElementById('output');
div.innerHTML = "ERROR: " + error.message;
}
google.script.run.withFailureHandler(onFailure)
.getUnreadEmails();
</script>
</head>
<body>
<div id="output"></div>
</body>
</html>
Related
I'm checking for a token in the boot() method and catching Invalid Tokens. How can I return some response in the case of an invalid token?
Here's my code:
public function boot(Authenticator $authenticator)
{
Auth::viaRequest('auth-token', function ($request) use ($authenticator) {
$bearerToken = $request->bearerToken();
if ($bearerToken) {
try {
return $authenticator->getUser($bearerToken);
} catch (InvalidTokenException $exeception) {
return response()->json(['token_invalid'], 400);
}
}
});
}
And it pips me the error:
Method Illuminate\Http\JsonResponse::getAuthIdentifier does not exist.
From the docs:
The second argument passed to the method should be a Closure that receives the incoming HTTP request and returns a user instance or, if authentication fails, null
So instead of returning a response object, return null:
if ($bearerToken) {
try {
return $authenticator->getUser($bearerToken);
} catch (InvalidTokenException $exeception) {
return null;
}
}
Im coming from a Java background where I use the throws keyword to lead an exception to the method calling another method. How can I do that I dart?
Method called:
void _updateCurrentUserEmail() async {
await FirebaseAuth.instance
.currentUser()
.then((FirebaseUser user) {
_email = user.email;
});
}
How it is called:
try {
_updateCurrentUserEmail();
} on Exception {
return errorScreen("No User Signed In!", barActions);
}
But it seems like the Exception is not caught, because I still get a NoSuchMethodException and the errorScreen is not shown.
While you correctly used try/catch, the exception is coming from an async function that you did not await.
try/catch only catch exceptions thrown within that block. But since you wrote:
try {
doSomethingAsyncThatWillTrowLater();
} catch (e) {
}
Then the exception thrown by the async method is thrown outside of the body of try (as try finished before the async function did), and therefore not caught.
Your solution is to either use await:
try {
await doSomethingAsyncThatWillTrowLater();
} catch (e) {
}
Or use Future.catchError/Future.then:
doSomethingAsyncThatWillTrowLater().catchError((error) {
print('Error: $error');
});
From the docs,
If the catch clause does not specify a type, that clause can handle any type of thrown object:
try {
breedMoreLlamas();
} on OutOfLlamasException {
// A specific exception
buyMoreLlamas();
} on Exception catch (e) {
// Anything else that is an exception
print('Unknown exception: $e'); <------------------
} catch (e) {
// No specified type, handles all
print('Something really unknown: $e');
}
Change it to this:
try {
_updateCurrentUserEmail();
} on Exception catch(e){
print('error caught: $e')
}
Another way to handle error is to do the following:
void _updateCurrentUserEmail() async {
await FirebaseAuth.instance
.currentUser()
.then((FirebaseUser user) {
_email = user.email;
throw("some arbitrary error");
});
.catchError(handleError);
}
handleError(e) {
print('Error: ${e.toString()}');
}
If currentUser()’s Future completes with a value, then()’s callback fires. If code within then()’s callback throws (as it does in the example above), then()’s Future completes with an error. That error is handled by catchError().
Check the docs:
https://dart.dev/guides/libraries/futures-error-handling
Throw
Here’s an example of throwing, or raising, an exception:
throw FormatException('Expected at least 1 section');
You can also throw arbitrary objects:
throw 'Out of llamas!';
throwing an exception is an expression, you can throw exceptions in => statements, as well as anywhere else that allows expressions:
void someMethod(Point other) => throw UnimplementedError();
here is example
main() {
try {
test_age(-2);
}
catch(e) {
print('Age cannot be negative');
}
}
void test_age(int age) {
if(age<0) {
throw new FormatException();
}
}
hope it helps..
In my Flutter app I'd like to make multiple network calls simultaneously and then do something when they all have finished. For this I use Future.wait(), which does what I want. However when a call fails it throws an exception, which is somehow not caught in the exception handler (i.e. uncaught exception).
When I do await _fetchSomeData() separately (outside Future.wait()) the exception does get called by the exception handler as expected.
Future<bool> someMethod() async {
try {
var results = await Future.wait([
_fetchSomeData(),
_fetchSomeOtherData()
]);
//do some stuf when both have finished...
return true;
}
on Exception catch(e) {
//does not get triggered somehow...
_handleError(e);
return false;
}
}
What do I need to do to catch the exceptions while using Future.wait()?
Update:
I have narrowed down the issue. Turns out if you use another await statement in the method that is called by the Future.wait() it causes the issue. Here an example:
void _futureWaitTest() async {
try {
//await _someMethod(); //using this does not cause an uncaught exception, but the line below does
await Future.wait([ _someMethod(), ]);
}
on Exception catch(e) {
print(e);
}
}
Future<bool> _someMethod() async {
await Future.delayed(Duration(seconds: 0), () => print('wait')); //removing this prevents the uncaught exception
throw Exception('some exception');
}
So if you either remove the await line from _someMethod() or if you just call _someMethod() outside of Future.wait() will prevent the uncaught exception. This is most unfortunate of course, I need await for an http call... some bug in Dart?
I have the Uncaught Exceptions breakpoints enabled. If I turn this off the issue seems to be gone. Perhaps it's an issue with the debugger. I am using Visual Studio Code and the latest flutter.
What do I need to do to catch the exceptions while using Future.wait()?
What I found out when I used the same code as you the code inside of each procedure which is used in Future.wait() must be wrapped with try/catch and on catch must return Future.error(). Also eagerError must be set to true.
try {
await Future.wait([proc1, ...], eagerError: true);
} on catch(e) {
print('error: $e')
}
/// Proc 1
Future<void> proc1() async {
try {
final result = await func();
} on SomeException catch(e) {
return Future.error('proc 1 error: $');
}
}
I think you are a bit mislead by the Future.wait() naming. Future.wait() returns another future that will have a List of elements returned by each future when it completes with success.
Now since the Future.wait() is still a future. You can handle it in two ways:
Using await with try catch.
Using onError callback.
Tis will be something like
Future.wait([futureOne, futureTwo])
.then((listOfValues) {
print("ALL GOOD")
},
onError: (error) { print("Something is not ok") }
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)?
Dart is an optional typed language. So the type of e is not required.
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.
In web app development I would like a consistent way to catch and report error conditions. For example, a database update routine may detect a variety of error conditions and ideally I would like the application to capture them and report gracefully. The code below din't work because retdiag is undefined when error is thrown...
function saveData(app,e) {
var db ;
var retdiag = "";
var lock = LockService.getPublicLock();
lock.waitLock(30000);
try {
// e.parameters has all the data fields from form
// re obtain the data to be updated
db = databaseLib.getDb();
var result = db.query({table: 'serviceUser',"idx":e.parameter.id});
if (result.getSize() !== 1) {
throw ("DB error - service user " + e.parameter.id);
}
//should be one & only one
retdiag = 'Save Data Finished Ok';
}
catch (ex) {
retdiag= ex.message // undefined!
}
finally {
lock.releaseLock();
return retdiag;
}
}
Is there a good or best practice for this is GAS?
To have a full error object, with message and stacktrace you have to build one, and not just throw a string. e.g. throw new Error("DB error ...");
Now, a more "consistent" way I usually implement is to wrap all my client-side calls into a function that will treat any errors for me. e.g.
function wrapper_(f,args) {
try {
return f.apply(this,args);
} catch(err) {
;//log error here or send an email to yourself, etc
throw err.message || err; //re-throw the message, so the client-side knows an error happend
}
}
//real client side called functions get wrapped like this (just examples)
function fileSelected(file,type) { return wrapper_(fileSelected_,[file,type]); }
function loadSettings(id) { return wrapper_(loadSettings_,[id]); }
function fileSelected_(file,type) {
; //do your thing
}
function loadSettings_(id) {
; //just examples
throw new Error("DB error ...");
}