Has Redux-Saga Got You Stuck In an Infinite Loop?

last updated: Oct 15th, 2016

You might start out with a saga that looks something like the following code.

No problem, it runs perfectly.

function* fetchSomethingSaga() {    // Run this saga forever    while (true) {        // Wait for a fetch request        const action = yield take(Action.FETCH_SOMETHING_REQUEST);        // Extract the id of what we need to fetch        const id = action.payload;        try {            // Make the API call            const thing = yield call(apiClient.get, `/thing/${id}`);            // We succeeded, return the thing            yield put(fetchSomethingSuccess(thing));        }        catch (err) {            // We failed, report the error            yield put(fetchSomethingFailure(err));        }    }}

At some point, you decide to replace take with takeEvery so your saga can handle concurrent requests. Or you replace it with takeLatest so you can process the most recent request.

But... your events start firing in an infinite loop. Hey, what gives?

Problem Code

function* fetchSomethingSaga() {    while (true) {        yield takeEvery(Action.FETCH_SOMETHING_REQUEST, fetchSomething);    }}function* fetchSomething(action) {    const id = action.payload;    try {        const something = yield call(apiClient.get, `/something/${id}`);        yield put(fetchSomethingSuccess(something));    catch (err) {        yield put(fetchSomethingFailure(err));    }}

The problem is that takeEvery/takeLatest were put in a loop, which is unnecessary because they already have a loop internally.

The Solution

Fix your outer saga by removing the loop.

function* fetchSomethingSaga() {    yield takeEvery(Action.FETCH_SOMETHING_REQUEST, fetchSomething);}

And have a quick refresher on takeEvery from the redux-saga documentation.

Happy coding!

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