如何实现异步循环(JS)
如何实现异步循环(JS)
提问于 2018-08-02 05:00:00
我有一个for each循环，我在其中检查一些东西。此检查是异步的，当此检查为false时，我希望中断循环。下面是我的代码：
addReservation(reservation: Reservation) {
this.deskService.loadDesksWhereRangeGreater(reservation.persons).subscribe(
desks => {
if (desks.length > 0) {
for (const desk1 of desks) {
console.log('checking');
if (this.checkForAvailability(desk1, reservation)) {
console.log('found');
}
}
}
}
);
}
async checkForAvailability(desk: Desk, reservation: Reservation) {
await this.db.collection('Desks').doc(desk.id)
.collection('Reservations', ref => ref.where('timestamp', '<=', reservation.timestamp + this.reservationDelta)
.where('timestamp', '>', reservation.timestamp - this.reservationDelta))
.valueChanges().subscribe(reservations => {
if (reservations.length === 0) {
console.log('reservation possible for ' + desk.nr);
return true;
} else {
console.log(desk.nr + ' Belegt');
return false;
}
});
}然而，await部件并不能真正工作。它只是在循环中迭代，而不是在每次迭代中等待异步函数。
回答 1
Stack Overflow用户
回答已采纳
发布于 2018-08-02 05:16:20
你需要从checkForAvailability中await出结果
addReservation(reservation: Reservation) {
this.deskService.loadDesksWhereRangeGreater(reservation.persons).subscribe(
async desks => {
if (desks.length > 0) {
for (const desk of desks) {
const available = await this.checkForAvailability(desk, reservation)
if (!available) { break }
}
}
}
);
}
checkForAvailability(desk: Desk, reservation: Reservation) {
// here, you need to return a promise
return new Promise(resolve => {
this.db.collection('Desks').doc(desk.id)
.collection('Reservations', ref => ref.where('timestamp', '<=', reservation.timestamp + this.reservationDelta)
.where('timestamp', '>', reservation.timestamp - this.reservationDelta))
.valueChanges().subscribe(reservations => {
resolve(reservations.length === 0)
});
})
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/51642187
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