javascript - 我收到未处理的 promise 拒绝错误，但无法弄清楚原因

Question

const express = require('express');
const cors = require('cors');
const massive = require('massive');
const bodyParser = require('body-parser');
const config = require('../config');

const app = express();

app.use(bodyParser.json());

//massive connection string to database

massive(config.dblink).then(db => {
    app.set('db', db)

    app.get('db').seed_file().then(res => {
        console.log(res)
    })
}).catch(err => {
    console.log(err)
});

const port = 3001;
app.listen(port, () => {console.log(`the server is listening on ${port}`)})

我收到以下错误:

(node:173676) UnhandledPromiseRejectionWarning: Unhandled promise rejection 
(rejection id: 2): error: syntax error at or near "{"                                           
(node:173676) [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.

我还没弄清楚哪里出了问题。我看过多个不同的例子，但看不出问题所在。在我的 seed_file promise 之后，我有一个 .catch。

有什么想法吗？

Answer 1

I'm getting an Unhandled Promise Rejection error but can't figure out why

您收到此警告是因为您有未处理的 promise 拒绝 :)。外部 catch() 方法不处理嵌套的 promise 拒绝，因此两个选项可能是:

1) 在嵌套的 promise 上使用 return，它将被外部 catch() 捕获:

massive(config.dblink).then(db => {
    app.set('db', db)
    return app.get('db').seed_file().then(res => {
        console.log(res)
    });
}).catch(err => console.log(err) });

2) 使用内部 catch() 以不同方式处理嵌套拒绝:

massive(config.dblink).then(db => {
    app.set('db', db)
    app.get('db').seed_file().then(res => {
        console.log(res)
    }).catch(err => console.log(err) });
}).catch(err => console.log(err) });

演示:

function doPromise(someText, flag) {
  return new Promise(function(resolve, reject) {
    setTimeout(function() {
      flag ? resolve(someText) : reject(someText);
    }, 500);
  });
}

/* The following sample demostrates unhandled rejection */
doPromise('this will resolve', true).then(function(res1) {
  console.log(res1);
  doPromise('this is unhandled promise rejection', false).then(function(res2) {
    console.log(res2);
  });
});

/* The following sample demostrates handling nested promise rejection like explained in point 1) */
doPromise('1) this will resolve', true).then(function(res1) {
  console.log(res1);
  return doPromise('1) nested rejection catched from outside', false);
}).catch(err => console.log(err));


/* The following sample demostrates handling nested promise rejection like explained in point 2) */
doPromise('2) this will resolve', true).then(function(res1) {
  console.log(res1);
  doPromise('2) nested rejection catched from inside', false).catch(err => console.log(err));
}).catch(err => console.log(err));