如何在一個生成函數中使用一個高階函數的變量？

Question

需要使用email = user.email在newcomment['comments/'+id] = {id,comment,email,date} ，但我不能使用email = yield user.email或yield auth.onAuthStateChanged(user => {email = user.email})和電子郵件歸因與空newcomment 。 我該怎么做？

export function* createComments(action){  
let email = null
try{
    auth.onAuthStateChanged(user => {
       email =  user.email
    })
    const id = yield database.ref().child("comments").push().key
    let date = new Date()
    date = yield date.getDate()+"/"+(date.getMonth()+1)+"/"+date.getFullYear()
    const newcomment = {}
    const comment = action.comment
    newcomment['comments/'+id] = {
        id,
        comment,
        email,
        date
    }
    database.ref().update(newcomment)
    yield put(ActionCreator.createCommentsSuccess(newcomment))
}catch({message}){
    yield put(ActionCreator.createCommentsFailure(message))
}

}

Answer 1

只要您只對第一次使用用戶調用onAuthStateChanged回調感興趣，您只需將其轉換為Promise：

const user = yield new Promise(resolve => {
  const unsub = auth.onAuthStateChanged(user => {
    if (user) {
      resolve(user);
      unsub();
    }
  });
});