在saga中监听动作的最佳方式:`while(true)take()`vs`while(take())`vs`takeEvery()`

Question

我见过传奇以三种方式听取行动:

1. while(true)take()

function* onUserDetailsRequest() {
  while(true) {
    const { userId } = yield take(USER_DETAILS_REQUESTED);
    const response = yield call(fetchUserDetails, userId);
    put(USER_DETAILS_RECEIVED, response);
  }
}    

2. while(take())

function* onUserDetailsRequest() {
  while(yield take(USER_DETAILS_REQUESTED)) {
    const userId = yield select(userSelectorFn);
    const response = yield call(fetchUserDetails, userId);
    put(USER_DETAILS_RECEIVED, response);
  }
}    

3. takeEvery()

function* onUserDetailsRequest() {
  yield takeEvery(USER_DETAILS_REQUESTED, function* (action) {
    const { userId } = action;
    const response = yield call(fetchUserDetails, userId);
    put(USER_DETAILS_RECEIVED, response);
  }
}

各自的优点和缺点是什么？在哪种情况下我们应该使用另一种情况？

Answer 1

用代码清除@ AlexM的答案.

cat test.js

const { createStore, applyMiddleware } =require('redux')
const createSagaMiddleware =require('redux-saga').default
const { takeEvery ,take,fork}=require('redux-saga/effects') 
const {delay} =require('redux-saga')
const sagaMiddleware = createSagaMiddleware()
const reducer=(state=[],action)=>{return [...state,action.type];}
const store = createStore(
    reducer,
    applyMiddleware(sagaMiddleware)
)
function* takeSaga() {
  while(true){
    const action=yield take('testTake')
    console.log(action)
    yield delay(1000)
  }
}

function* takeEverySaga() {
    yield takeEvery('testTakeEvery',function* (action){
        console.log(action)
        yield delay(1000)
    })
}

function* takeSagaWithFork() {
    while(true){
      const action=yield take('testTakeWithFork')
      yield fork(function*(){
        console.log(action)
        yield delay(1000)
      })
    }
}

sagaMiddleware.run(takeSaga)
sagaMiddleware.run(takeEverySaga)
sagaMiddleware.run(takeSagaWithFork)

const main=async ()=>{
    store.dispatch({type: 'testTake'})
    store.dispatch({type: 'testTake'})
    store.dispatch({type: 'testTakeEvery'})
    store.dispatch({type: 'testTakeEvery'})
    store.dispatch({type: 'testTakeWithFork'})
    store.dispatch({type: 'testTakeWithFork'})
}

main();

用node test.jswill输出运行上面的代码

{ type: 'testTake' }
{ type: 'testTakeEvery' }
{ type: 'testTakeEvery' }
{ type: 'testTakeWithFork' }
{ type: 'testTakeWithFork' }

你看得到差别吗？takeSaga当第二个testTake动作被调度时,任务正在休眠,因此takeSaga完全忽略了第二个testTake动作.然而,对于takeEverySaga和takeSagaWithFork,每当它收到一个testTakeEvery动作时,一个新的任务被分叉,所以他们在自己的任务"线程"中睡觉,所以不会错过新的动作.因此,takeEvery基本上与while(true)+ take+ 相同fork.