How do I debug a saga?

Question

How can I debug this problem? I can find no information to follow.

I have the following saga:

    export function* generateSoftwareLicenseCode({distributor, licenseType, duration}: GenerateSoftwareLicenseCodeAction) {
        const username = getUsername();
        const jwtToken = yield call(getJwtToken, username);
    
        const link = new HttpLink({
            uri: getGraphqlEndpointUrl,
            headers: {
                'x-api-key': getApiKey(),
                'Authorization': jwtToken,
            },
        });
        const client = new ApolloClient({
            link: link,
            cache: new InMemoryCache(),
        });
    
        try {
            yield put(setStatusMessage('Generating license code...', 'info'));
    
            yield client.mutate({
                /* tslint:disable */
                mutation: gql`
                    }
                    mutation licensemutation($distributor: String!, licenceType: String!, duration: String, userId: String) {
                        addLicenseCodeOneTimeUsage(distributor: $distributor, licenseType: $licenseType, duration: $duration, userId: $userId) {
                            code
                        }
                    }
                `,
                /* tslint:enable */
                variables: {
                    userId: username,
                    distributor: distributor,
                    licenseType: licenseType,
                    duration: duration,
                },
            });
            const doneMessage = 'License code successfully generated';
            yield put(generateSoftwareLicenseCodeSucceeded(doneMessage));
        } catch (error) {
            const errors = error.networkError.result.errors;
            yield put(generateSoftwareLicenseCodeFailed(filterErrorMessage(errors)));
        }
    }

    export function* softwareLicenseCodesSagas() {
        const generateSoftwareLicenseCodeWatcher = yield takeLatest(GENERATE_SOFTWARE_LICENSE_CODE_ACTION, generateSoftwareLicenseCode);
        yield take(LOCATION_CHANGE);
        yield put(clearMessages());
        yield cancel(generateSoftwareLicenseCodeWatcher);
    }

The try block throws an error. The error in the catch block is undefined.

The console shows uncaught at at at at b TypeError: Cannot read property 'result' of undefined

Stepping through the code takes me though a bunch of library code that I don't understand.

Answer 1

If this saga is being executed within the browser, you can use the debugger to pause the executing and inspect variables as you normally would. If it is on the server, console.log will work just fine.

In terms of the error, it is best practice to always use the redux-saga call method when yielding executed functions within a saga. Therefore, you should change it to be:

    yield call(client.mutate, options)