redux-saga：函数被调用两次

Question

I am toggling visibility of a modal in react based on result of some logic performed in saga middleware by dispatching action from saga.

I went through:

• Action is being dispatched twice on github

• takeEvery/takeLatest is executed twice even though action dispatched only once

  • Wasn't very helpful.

Store

export default function configureStore(preloadedState) {
  const sagaMiddleware = createSagaMiddleware();
  const middlewares = [..otherMiddleware, sagaMiddleware, ...someMoreMiddlewares];

  const store = createStore({
    // other configuration,
    // middleWares
  })

  sagaMiddleware.run(rootRunner);
  return store;
}

Reducer :

const initialState = {
  activeSwitch: '1',
  modalVisibility: false,
}

export default function reducer(state = initialState, action) {
  switch (action.type) {
    case 'TOGGLE_MODAL':
      return state.set('modalVisibility', !state.get('modalVisibility'));
    case 'UPDATE_ACTIVE_SWITCH':
      // update active switch
    default:
      return state;
  }
}

Action :

export const switchOption = payload => ({
  type: 'SWITCH_OPTION',
  payload,
})

export const toggleModal = () => ({
  type: 'TOGGLE_MODAL',
})

export const updateActiveSwitch = payload => ({
  type: 'UPDATE_ACTIVE_SWITCH',
  payload,
})

Component :

import switchOption from 'action';

function Component(props) {
  return <div onClick={props.switchOpt(somePayloadParameter)} />;
}

const mapDispatchToProps = state => ({
  switchOpt: (somePayloadParameter) => dispatch(switchOption(somePayloadParameter)),
})

export default connect(null, mapDispatchToProps)(Component);

RootSaga :

export default function* rootRunner() {
  yield all([ fork(watcher) ])
}

Saga :

function* worker(payload) {
  console.log('hey');
  yield put({'TOGGLE_MODAL'})
  // Perform some task and wait for modal ok button click
  yield take('MODAL_OK');
  if (taskSuccess) {
  yield put({ type: 'UPDATE_ACTIVE_SWITCH', someValue});
  yield put({ type: 'TOGGLE_MODAL'}};
}

export default function* watcher() {
  while(true) {
    yield actionObj = yield take('SWITCH_OPTION');
    yield call(worker, actionObj.payload);
  }
}

Modal is never visible as 'TOGGLE_MODAL' is being dispatched twice from saga, as a result of watcher calling worker twice.

If I put a debugger just after while(true) { in watcher , on page load , that breakpoint is hit twice.

Even if I remove every line from worker , it is still running twice.

Why is my saga code running twice?

---

EDIT

Component :

import switchOption from 'action';

function Component(props) {
  return <div onClick={props.switchOpt(somePayloadParameter)} />;
}

const mapDispatchToProps = state => ({
  // switchOption is action from action.js
  switchOpt: (somePayloadParameter) => dispatch(switchOption(somePayloadParameter)),
})

export default connect(null, mapDispatchToProps)(Component);

Redux monitor middleware logs to the console in dev tools following three actions, after executing saga function when it is called onClick for the first time:

• 'SWITCH_OPTION'
• 'TOGGLE_MODAL' --> with modalVisibility set to true
• 'TOGGLE_MODAL' --> with modalVisibility set to false

Now the click on div becomes useless as MODAL never popped up and there is no OK button to click on.

Answer 1

Right now Component is calling props.switchOpt every time it renders. Instead, create a new function that can be passed by reference and is then called with onClick :

function Component(props) {
  return <div onClick={() => { props.switchOpt(somePayloadParameter); }} />;
}

Answer 2

Use takeLatest helper. It allows the saga generator to only take the latest request