使用Promises时，每个then（）应该返回一个值或抛出

Z时代
2024-01-10
分类：问答

从请求返回之前，我有一些异步方法需要等待完成。我正在使用Promises，但我不断收到错误消息：

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

为什么这令人高兴？这是我的代码：

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
})

回答：

只要避免Promise构造函数反模式-promise-construction-antipattern-and-how-to-avoid-

it)！如果您不调用resolve而是返回一个值，那么您将需要进行一些操作return。该then方法应该用于链接：

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 => { … });
})