cancellation too presumptive?

Just some food for thought…

Nevertheless, a warning is logged into the console in case a cancelled task omitted to handle a cancellation exception.

I have quite a few instances where one saga spawns a fetcher function, and that fetcher func then invokes the actual function doing the xhr. This is to keep functions lean and “doing one thing”. Maybe I want to transform the parameters or data before/after fetching, or maybe I want to check status codes and validate returned values versus nulls, etc.

    function doFetch(params) {
        yield xhr(url, params)
    }

    function* fetch(params) {
        const { statusCode, body } = yield call(doFetch, params)

        if (statusCode > 499) {
            return null
        }

        const data = body.someData

        // ... do some transformations on the data

        return {
            transformedData
        }
    }

    function* fetchSomeStuff() {
        yield put(START_FETCH)

        // ...maybe configure some parameters

        const results = yield call(fetch, params)

        // ...do some data transforms on results

        yield put(FETCH_SUCCESS, results)
    }

When I want to sure up this code with some error handling, in order to avoid a console.warn by redux-saga I have to put in a try/catch for every step along the saga. This is fairly inconvenient to have to handle a thrown saga cancelled exception at every invocation, particularly because I only want to use the catch to “cleanup” in one of the cases:

    function doFetch(params) {
        let req
        try {
            return (yield req = xhr(url, params))
        } catch (e) {
            if (e instanceof SagaCancellationException) {
                req.abort()
            } else {
                throw e
            }
        }
    }

    function* fetch(params) {
        // doesn't have to handle errors, since there's nothing to do and the
        // caller handles anything that might be thrown... 
        try {
            // ... same code as above
        } catch (e) {
            // there's nothing to do here except stop the console.warn() from showing up
        }
    }

    function* fetchSomeStuff() {
        try {
            yield put(START_FETCH)

            // ...maybe configure some parameters

            const results = yield call(fetch, params)

            // ...do some data transforms on results

            yield put(FETCH_SUCCESS, results)
        } catch (e) {
            // capture SagaCancellationException, but throw any js errors
            if (!e instanceof io.SagaCancellationException) {
                console.error(e)
            }
        }
    }

[yelouafi]

I’m thinking of making this an opt-in behavior. Provide some config argument, so the developer can choose to disable the console warnings

[yelouafi]

@aft-luke yes. Included with the new 0.6.0