每个then（）应该在使用Promises时返回一个值或throw

本文介绍了每个then（）应该在使用Promises时返回一个值或throw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

在我从请求返回之前，我需要等待完成的一些异步方法。我正在使用Promises，但我一直收到错误：

I have a few async methods that I need to wait for completion before I return from the request. I'm using Promises, but I keep getting the error:

Each then() should return a value or throw // promise/always-return

为什么这样开心？这是我的代码：

Why is this happpening? This is my code:

router.get('/account', function(req, res) { var id = req.user.uid var myProfile = {} var profilePromise = new Promise(function(resolve, reject) { var userRef = firebase.db.collection('users').doc(id) userRef.get() .then(doc => { // Error occurs on this line if (doc.exists) { var profile = doc.data() profile.id = doc.id myProfile = profile resolve() } else { reject(Error("Profile doesn't exist")) } }) .catch(error => { reject(error) }) }) // More promises further on, which I wait for })

推荐答案

只需避免 无极构造函数反模式！如果你不打电话给解决但是返回一个值，那么你将有一些东西要返回。 然后方法应该用于链接，而不仅仅是订阅：

Just avoid the Promise constructor antipattern! If you don't call resolve but return a value, you will have something to return. The then method should be used for chaining, not just subscribing:

outer.get('/account', function(req, res) { var id = req.user.uid var userRef = firebase.db.collection('users').doc(id) var profilePromise = userRef.get().then(doc => { if (doc.exists) { var profile = doc.data() profile.id = doc.id return profile // I assume you don't want to return undefined // ^^^^^^ } else { throw new Error("Profile doesn't exist") // ^^^^^ } }) // More promises further on, which I wait for: // profilePromise.then(myProfile => { … }); })