async function filterusers(users){
let usersfiltered=[]
for(var i = 0;i < users.length; i++){
let userref = db.collection('usernames').doc(users[i]);
let getDoc = userref.get()
.then(doc => {
if (doc.exists) {
usersfiltered.push(users[i])
}
})
}
return await usersfiltered;
}
filterusers(users).then(console.log);
我希望等待过滤结果,但它总是在返回结果之前打印空白数组即。
async function filterusers(users){
let usersfiltered=[]
// You should use let or const instead of var.
for(let i = 0;i < users.length; i++){
// I believe getting doc needs await.
let userref = await db.collection('usernames').doc(users[i]);
await userref.get()
.then(doc => {
if (doc.exists) {
usersfiltered.push(users[i])
}
})
}
return usersfiltered;
}
filterusers(users).then(console.log);
首先,您必须使用Array.map
将用户数组转换为 Promises(异步操作(数组:
const checkUserPromises = users.map((user) => {
const userref = db.collection("usernames").doc(user);
return userref.get().then((doc) => {
if (doc.exists) {
return user;
} else {
return null;
}
});
});
然后,您需要Promises.all
await
这些承诺:
const checkedUsers = await Promise.all(checkUserPromises);
最后,您可能希望过滤掉不存在的用户:
const existingUsers = checkedUsers.filter((user) => user !== null);
await 应该与 Promise 一起使用
async function filterusers(users) {
let usersfiltered = [];
for (let i = 0; i < users.length; i++) {
let userref = db.collection("usernames").doc(users[i]);
let getDoc = await userref.get();
if (getDoc.exists) {
usersfiltered.push(users[i]);
}
}
return usersfiltered;
}
let filterdUsers = filterusers(users);
console.log(filterdUsers);
首先,不要将async/await与.then混合使用。
其次,使用新的 ES6for 循环,使代码在 async/await 中正常工作。
async function filterusers(users) {
let usersfiltered = [];
filterusers(users).then(console.log);
for (const user of users) {
let userref = db.collection('usernames').doc(user);
const doc = await userref.get();
if (doc.exists) {
usersfiltered.push(user);
}
}
return await usersfiltered;
}
通过将await
移动到userref.get()
之前自己解决了它
async function filterusers(users){
let usersfiltered=[]
for(var i = 0;i < users.length; i++){
let userref = db.collection('usernames').doc(users[i]);
let getDoc = await userref.get()
.then(doc => {
if (doc.exists) {
usersfiltered.push(users[i])
}
})
}
return usersfiltered;
}
filterusers(users).then(console.log);