UnhandledPromiseRejectionWarning，即使代码在async / await中进行了try / catch

Question

我意识到这似乎是其他问题的重复，但是在发布此问题之前，我已经查看了我可以找到的每个建议的SO问题，并且我正在此特定情况下寻求帮助，因为其他答案均无济于事对我来说。

我有一个Node / Express应用程序，该应用程序正在初始化要由REST API使用的单个MongoDB连接。第一步是连接到MongoDB实例。如果初始连接失败，它将按预期抛出错误。我正在使用async / await及其内部的try / catch块来处理它。我到过的所有地方都说，这足以捕获这些异步/等待的诺言拒绝，但是无论我在哪里.catch()或尝试/捕获我的代码，我都始终遇到关于UnhandledPromiseRejection的错误（如建议在其他SO帖子中。）

例如，在此链接中，我有与错误处理部分所述的内容几乎相同的东西，但问题仍然存在。

https://javascript.info/async-await

这是错误（我知道是什么导致了错误本身-我现在已经停止了MongoDB服务-但我正在尝试解决未处理的承诺拒绝错误）：

(node:15633) 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(). (rejection id: 1) (node:15633) [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. (node:13802) UnhandledPromiseRejectionWarning: MongoNetworkError: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017] at Pool.<anonymous> (/home/allen/scripts/lysi/eosMain/node_modules/mongodb-core/lib/topologies/server.js:562:11) at Pool.emit (events.js:189:13) at Connection.<anonymous> (/home/allen/scripts/lysi/eosMain/node_modules/mongodb-core/lib/connection/pool.js:316:12) at Object.onceWrapper (events.js:277:13) at Connection.emit (events.js:189:13) at Socket.<anonymous> (/home/allen/scripts/lysi/eosMain/node_modules/mongodb-core/lib/connection/connection.js:245:50) at Object.onceWrapper (events.js:277:13) at Socket.emit (events.js:189:13) at emitErrorNT (internal/streams/destroy.js:82:8) at emitErrorAndCloseNT (internal/streams/destroy.js:50:3) at process._tickCallback (internal/process/next_tick.js:63:19)

这是我的代码：

exports.mongoConnect = async (dbName, archiveDbName, userName, password) => {

    // Auth params
    const user = encodeURIComponent(userName);
    const pass = encodeURIComponent(password);
    const authMechanism = 'DEFAULT';

    // Connection URL
    const url = `mongodb://${user}:${pass}@localhost:27017?authMechanism=${authMechanism}&authSource=admin`;
    let client;

    try {
        // Use connect method to connect to the Server
        client = await MongoClient.connect(url, { useNewUrlParser: true, poolSize: 10, autoReconnect: true, reconnectTries: 6, reconnectInterval: 10000 }).catch((e) => { console.error(e) });

        db = client.db(dbName);
        archiveDb = client.db(archiveDbName);

        console.log(`Succesfully connected to the MongoDb instance at URL: mongodb://localhost:27017/ with username: "` + client.s.options.user + `"`);
        console.log(`Succesfully created a MongoDb database instance for database: "` + db.databaseName + `" at URL: mongodb://localhost:27017/`);
        console.log(`Succesfully created a MongoDb database instance for database: "` + archiveDb.databaseName + `" at URL: mongodb://localhost:27017/`);
    } catch (err) {
        console.log(`Error connecting to the MongoDb database at URL: mongodb://localhost:27017/` + dbName);
    }
}

像这样从app.js调用的

：

mongoUtil.mongoConnect('myDb', 'myArchiveDb', 'myUser', 'myPassword');

我什至尝试将这一行放在try / catch块中，或者将诺言样式.catch()添加到它的末尾，而无需进行任何更改。

我似乎无法弄清为什么它仍然抱怨没有处理承诺拒绝。

编辑：

这是整个app.js文件：

var createError = require('http-errors');
var express = require('express');
var path = require('path');
var cookieParser = require('cookie-parser');
var logger = require('morgan');

var cors = require('cors');
var app = express();

const MongoClient = require('mongodb').MongoClient;
// This is where the mongo connection happens
var mongoUtil = require( './services/mongoUtil' );
var bluebird = require('bluebird');

const jwt = require('./helpers/jwt');

var api = require('./routes/api.route')

// view engine setup
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'ejs');

app.use(cors());
app.use(logger('dev'));
app.use(express.json()); 
app.use(express.urlencoded({ extended: false }));
app.use(cookieParser());
app.use(express.static(path.join(__dirname, 'public')));

app.use('/api', api);

// use JWT auth to secure the api
app.use(jwt());

app.use('/users', require('./users/users.controller'));

MongoClient.Promise = bluebird

mongoUtil.mongoConnect('myDb', 'myArchiveDb', 'username', 'password');

app.use(function(req, res, next) {
  res.header("Access-Control-Allow-Origin", "*");
  res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  res.header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
  next();
});

// catch 404 and forward to error handler
app.use(function(req, res, next) {
  next(createError(404));
});

// error handler
app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};

  // render the error page
  res.status(err.status || 500);
  res.render('error');
});

module.exports = app;`

Answer 1

我测试了您的代码，如下面的屏幕截图所示，它可以正常工作。我认为问题在于调用mongoConnect（）的原因

Answer 2

您正在以同步方式从app.js调用connect，因此您的async/await方法将不起作用。您可以使用sleep函数对其进行测试：

let sleep = () => {
  return new Promise(function(resolve, reject) {
    setTimeout(function(){
      console.log('Finished sleeping');
      resolve();
    }, 2000)
  })
}

exports.mongoConnect = async (dbName, archiveDbName, userName, password) => {
  await sleep() // sleep two seconds
  // rest of your mongoConnect code
})

然后在连接后在app.js中添加一个日志：

mongoUtil.mongoConnect('myDb', 'myArchiveDb', 'username', 'password');
console.log('Finished connection');

您将在控制台中获得以下输出：

Finished connection // You can see the code doesnt wait to mongo to connect
[After 2 seconds]
Finished sleeping // After this sleep log it will start connecting...

要解决此问题，您需要以异步方式执行app.js：

请注意，不建议使用顶级异步功能，但我希望您看到此错误

(async () => {
    // rest of your app.js
    await mongoUtil.mongoConnect('myDb', 'myArchiveDb', 'username', 'password');
    console.log('Finished connection attempt');
    // rest of your app.js
})()

然后我在控制台遇到的错误是（无警告！）：

{ MongoNetworkError: failed to connect to server [localhost:27017] on first connect [MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017]
    at Pool.<anonymous> (/node_modules/mongodb-core/lib/topologies/server.js:564:11)
    at Pool.emit (events.js:182:13)
    at Connection.<anonymous> (/node_modules/mongodb-core/lib/connection/pool.js:317:12)
    at Object.onceWrapper (events.js:273:13)
    at Connection.emit (events.js:182:13)
    at Socket.<anonymous> (/node_modules/mongodb-core/lib/connection/connection.js:246:50)
    at Object.onceWrapper (events.js:273:13)
    at Socket.emit (events.js:182:13)
    at emitErrorNT (internal/streams/destroy.js:82:8)
    at emitErrorAndCloseNT (internal/streams/destroy.js:50:3)
    at process._tickCallback (internal/process/next_tick.js:63:19)
  name: 'MongoNetworkError',
  errorLabels: [ 'TransientTransactionError' ],
  [Symbol(mongoErrorContextSymbol)]: {} }
Error connecting to the MongoDb database at URL: mongodb://localhost:27017/myDb
Finished connection attempt