每个then（）应该在使用Promises时返回一个值或throw [英] Each then() should return a value or throw when using Promises

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 => { … });
})

这篇关于每个then（）应该在使用Promises时返回一个值或throw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！