函数内部的函数不等待javascript中的承诺

本文介绍了函数内部的函数不等待javascript中的承诺的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

对不起，如果我的标题不是很明确，我不知道该如何正确解释.我正在尝试为使用环回3和mongodb的应用程序使用独特的功能.它似乎工作正常，但是我的端点不会在函数内部命中返回值.这是我的代码

Sorry if my title is not very explicit I dont know how to explain this properly. I am trying to use the distinct function for my app that uses loopback 3 and mongodb. It seems to work right but my endpoint wont hit the return inside my function. This is my code

const distinctUsers = await sellerCollection.distinct('userId',{ hostId : host.id, eventId:{ "$ne" : eventId } }, async function (err, userIds) {; if(!userIds || userIds.length ==0) return []; const filter = { where:{ id: { inq: userIds } } }; console.log("should be last") return await BPUser.find(filter); }); console.log(distinctUsers); console.log("wtf??"); //return [];

如果我取消对return []的注释，它将发送返回信息，稍后它将显示应该是最后一个，因此即使我没有返回信息，它也似乎完成了.现在正在等待响应.我不喜欢我的代码的外观，因此，如何使它看起来更好的任何指针，我都会接受.

If I uncomment the return [] it will send the return and later it will show the should be last, so even when I dont have the return it seems to finish. It is now waiting for the response. I dont like the way my code looks so any pointer of how to make this look better I will take it.

推荐答案

看起来 sellerCollection.distinct 将回调作为其参数之一，因此，您不能>将 async/await 与回调样式函数一起使用，因为这不是承诺.

It looks like the sellerCollection.distinct takes a callback as one of it's parameters, therefore, you cannot use async/await with a callback-style function, since it's not a promise.

如果您想使用 async/await :

function findDistinct(hostId, eventId) { return new Promise((resolve, reject) => { sellerCollection.distinct( 'userId', { hostId, eventId: { "$ne": eventId } }, function (error, userIds) { if (error) { reject(error); return; } if (!userIds || userIds.length === 0) { resolve([]); return; } resolve(userIds); } ) }) }

然后，您可以将新功能与 async/await 一起使用，例如:

Then, you can use this new function with async/await like such:

async function getDistinctUsers() { try { const hostId = ... const eventId = ... const distinctUsers = await findDistinct(hostId, eventId) if (distinctUsers.length === 0) { return } const filter = { where: { id: { inq: userIds } } } const bpUsers = await BPUser.find(filter) // assuming it's a promise console.log(bpUsers) } catch (error) { // handle error } }