如何避免JavaScript中的异步函数? [英] How to avoid async functions in javascript?
问题描述
function CanPurchase() {
return new Promise(function(resolve, reject){
var name = document.getElementById('name').value;
var civilNumber = document.getElementById('civilNumber').value;
var canPurchase_query = db.collection("observer").doc("purchase_record").collection("record_set").where("name",
"==", name).where("civilNumber", "==", civilNumber);
var result = "";
canPurchase_query
.get()
.then(function (querySnapshot) {
querySnapshot.forEach(function (doc) {
// doc.data() is never undefined for query doc snapshots
result += doc.data().time;
});
if (result) {
console.log("canPurchase", false);
alert(false);
resolve(false);
} else {
alert(true);
console.log("canPurchase", true);
resolve(true);
}
})
.catch(function (error) {
alert(false);
console.log("Error getting documents: ", error);
resolve(false);
});
});
}
function StoreBuyerListInDB() {
var serialNumber = document.getElementById("serialNumber3").value;
var name = document.getElementById("name").value;
var count = document.getElementById("count3").value;
var civilNumber = document.getElementById("civilNumber").value;
var canPurchase = CanPurchase().then(function(resolvedData){
return resolvedData;
});
sleep(3222);
//DB에 시리얼넘버, 이름, 개수, 주민번호 넣기
var docRef = db.collection("users").doc(firebaseEmailAuth.currentUser.uid);
var docRef2 = db.collection("users").doc(firebaseEmailAuth.currentUser.uid).collection("buyers");
var docRef3 = db.collection("observer").doc("purchase_record").collection("record_set");
//로그인된 사용자가 seller인지 확인
docRef.get().then(function (doc) {
if (doc.exists) {
if (doc.data().index != "seller") {
alert('seller가 아니라면 등록할 수 없습니다! 돌아가세요!');
return;
}
console.log("Document data:", doc.data());
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
return;
}
}).catch(function (error) {
console.log("Error getting document:", error);
});
//어느 칸이라도 비어있으면 안됨
if (!serialNumber || !name || !count || !civilNumber) {
alert('제대로 입력해주세요!');
return;
}
//갯수가 0개이상 3개이해
else if (count < 0 || count >= 3) {
alert('1인당 3개 이하의 마스크만 구매 가능합니다! 다시 입력해주세요!');
return;
}
//주민번호 유효성
else if (!ValidateCivilNumber(civilNumber)) {
alert('주민번호가 유효하지 않습니다.');
return;
}
//전체 구매자 db에 이름, 주민번호가 같은사람이 있을경우 등록 불가
else if (!canPurchase) {
alert('이번주에 이미 구매하셨습니다.');
return;
}
else{
//해당seller의 db에 저장
docRef2.add({
name: name,
serialNumber: serialNumber,
count: count,
civilNumber: civilNumber,
time: firebase.firestore.FieldValue.serverTimestamp()
})
.then(function (docRef) {
console.log("Document written with ID: ", docRef.id);
alert("seller 저장 완료!");
setTimeout(GetDataFromDB(), 3000);
})
.catch(function (error) {
console.error("Error adding document: ", error);
alert("seller 저장 실패!");
});
//감사자인 observer db에 저장
docRef3.add({
name: name,
serialNumber: serialNumber,
count: count,
civilNumber: civilNumber,
time: firebase.firestore.FieldValue.serverTimestamp()
})
.then(function (docRef) {
console.log("Document written with ID: ", docRef.id);
alert("observer 저장 완료!");
setTimeout(GetDataFromDB(), 3000);
})
.catch(function (error) {
console.error("Error adding document: ", error);
alert("observer 저장 실패!");
});
}
}
我想知道用户可以使用CanPurchase()函数以及是否可以购买商品.但实际上，这是行不通的.
I wanna know user can purchase items or not by using CanPurchase() function and if process. But in real case, it doesn't work.
else if (!canPurchase) {
alert('이번주에 이미 구매하셨습니다.');
return;
}
在这里，它只是通过了这个逻辑.因此无论canPurchase变量是什么，它都会继续.因此，我搜索了一些避免此问题的方法.我用了诺言.但这也行不通.我该如何解决?非常感谢 ！！
here it just pass this logic. so whatever canPurchase variable is, it just go on. So I searched some ways to avoid this problem. I used promise. but also it doesn't work too. How can i solve it? Thank you so much !!
推荐答案
无法使调用异步API的代码同步运行.如果您想与基于云的(以及大多数其他现代)API进行交互，则必须学习如何使用异步调用.
There is no way to make code that calls an asynchronous API behave synchronously. If you want to interact with cloud-based (and most other modern) APIs, you will have to learn to work with asynchronous calls.
在您的情况下， CanPurchase 的代码可能会更简单，因为据我所知，您无需声明自己的承诺.应该是这样的:
In your case, the code for CanPurchase can be a bit simpler, as you don't need to declare your own promise as far as I can see. It should be something like this:
function CanPurchase() {
var name = document.getElementById('name').value;
var civilNumber = document.getElementById('civilNumber').value;
var canPurchase_query = db.collection("observer").doc("purchase_record")
.collection("record_set")
.where("name", "==", name)
.where("civilNumber", "==", civilNumber);
var result = "";
return canPurchase_query
.get()
.then(function (querySnapshot) {
querySnapshot.forEach(function (doc) {
result += doc.data().time;
});
return !result
})
.catch(function (error) {
return false;
});
});
因此，它不再具有自定义的 Promise ，而是从 then 和 catch 以及查询中返回值.这是使用诺言时的一种常见模式，称为冒泡结果.
So this no longer has a custom Promise, but instead returns the value from within then and catch and then the query. This is a common pattern when using promises, and is called bubbling up the results.
您现在可以使用以下命令调用此函数:
You can now call this function with:
canPurchase().then(function(result) {
if(!result) {
alert('이번주에 이미 구매하셨습니다.');
}
}
如果可以使用一些更现代的JavaScript功能，可以使用 async / await 使此代码看起来更熟悉:
If you're OK with using some more modern JavaScript feature, you can use async/await to make this code look a bit more familiar:
async function CanPurchase() {
...
}
let result = await canPurchase();
if(!result) {
alert('이번주에 이미 구매하셨습니다.');
}
请记住，这是围绕带有promise的现有流程的语法糖，并且不会改变这些是异步调用的事实.
Just keep in mind that this is syntactic sugar around the existing flow with promises, and does not change the fact that these are asynchronous calls.
这篇关于如何避免JavaScript中的异步函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
