我在承诺链中有 catch() 但仍然收到未处理的承诺拒绝

Question

我发现很多线程都有同样的问题，但几乎所有线程都没有 catch() 或错误地使用了 promise 链。我正在测试用户输入错误的密码或身份并且登录失败的情况。在我的代码中，我认为我使用 catch() 正确地使用了承诺链，但我仍然遇到未处理的承诺拒绝错误。该站点应显示类似于网站上的错误消息“密码错误”。

代码写在node.js和express.js

这是我的代码： app.js

app.post('/:login',(req,res)=>{
 const userId = req.body.userId;
 const userPw = req.body.userPW;
 try{
  if(userId.length<5&&userPw.length<5){
    throw "Id and password must be minimum 5 characters";
  }else if(userId.length>=5&&userPw.length<5){
    throw "Password must be minimum 5 characters";
  }else if(userId.length<5&&userPw.length>=5){
    throw "Id must be minimum 5 characters";
  }else{
    dbFile.checkIfUserExists(userId,userPw,res)
    .then((response)=>{
      console.log(response[0].userId);
      return response[0].userId;
    }).catch((errMessage)=>{
      console.log(errMessage);
      throw errMessage;
    })
  }
}
 catch(e){
  console.log(e);
  res.send({
    errorMessage:e
  })
 }
});

userListDB.js

const mysql = require('mysql');

function createMySQLConnection(){
    const connection = mysql.createConnection({
        host:'localhost',
        user:'root',
        password:'',
        database:'chatdatabase'
    });
    return connection;
}
function connectToDB(connection){
    try{
        connection.connect(function(err){
            if(err){
                throw "Sorry, something happened. Please try later";
            }
        })
    }catch(error){
        return error;
    }
}
module.exports={
    checkIfUserExists:function(id,pw,res){
        const connection = createMySQLConnection();
        if(connectToDB(connection)===undefined||connectToDB(connection)===null){
            const sql = "SELECT * FROM userlist WHERE userId=? AND password=?";
            return new Promise((resolve,reject)=>{
                connection.query(sql,[id,pw],(error,result)=>{
                    try{
                        if(error){
                            throw error;
                        }
                        else if(result.length===0){
                            throw "It seems like your id and password don't match. please try again with different id and password";
                        }
                        else{
                            resolve(result);
                        }
                    }catch(e){
                        reject(e);
                    }
                })
            })
        }
    }
}

我知道我没有进行密码加密，但我会在解决此问题后进行加密。正如您在代码中看到的，当用户发送 POST 登录请求时，app.js 中的 app.post 将验证数据，如果没有问题，它将从 [=] 调用 dbFile.checkIfUserExists 34=]。 dbUserList returns 一个承诺所以我在 app.post.

中用 .then().catch() 做了一个承诺链

但我还是得到了

It seems like your id and password don't match. please try again with different id and password
(node:7896) UnhandledPromiseRejectionWarning: It seems like your id and password don't match. please try again with different id and password
(Use `node --trace-warnings ...` to show where the warning was created)
(node:7896) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). To terminate the node process on unhandled promise rejection, use the CLI flag `--unhandled-rejections=strict` (see https://nodejs.org/api/cli.html#cli_unhandled_rejections_mode). (rejection id: 1)
(node:7896) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.

我发现 console.log 在 then().catch() 中工作，所以在两个 try catch 中应该没有任何问题，我不明白为什么我的代码仍然显示未处理的承诺拒绝

Answer 1

确实，您有一个未处理的承诺拒绝：

.catch((errMessage)=>{
  console.log(errMessage);
  throw errMessage;
})

.catch 位于承诺链的末尾，因此 returns 是一个承诺。现在，如果您进入 catch 回调和 throw，那么这将使该承诺处于拒绝状态，并且没有更多的处理程序来处理该拒绝。

你应该直接在那个地方发送而不是扔：

res.send({errorMessage: errMessage})

我在承诺链中有 catch() 但仍然收到未处理的承诺拒绝

I have catch() in promise chain but still gets unhandled promise rejection

javascript

node.js

promise

express