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UnhandledPromiseRejectionWarning when re-throw error from inner catch to outer catch

I use Node Js 12. I have below code and error. I want to re-throw err from inner catch and catch it in outer one. How to modify my code to achieve error re-throw?? Thanks.
function test() {
try {
// Some other code before promise chain below that could cause exception
return Promise.resolve()
.then(() => {
const e = new Error();
e.message = 'testtest';
e.statusCode = 404;
throw e;
})
.catch(err => {
console.log('==inner===', err);
throw err;
});
} catch (err) {
console.log('==outer===', err);
}
}
test();
Error
jfan#ubuntu2004:~/Desktop/temp/d$ node index.js
==inner=== Error: testtest
at /home/jfan/Desktop/temp/d/index.js:17:19 {
statusCode: 404
}
(node:34826) UnhandledPromiseRejectionWarning: Error: testtest
at /home/jfan/Desktop/temp/d/index.js:17:19
(node:34826) 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:34826) [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.
jfan#ubuntu2004:~/Desktop/temp/d$

SUGGESTION
// define an async function for the purpose of awating a promise inside the function
// optional useError parameter is used to trigger an error for testing purposes
// optional args parameter is for passing any additional parameters to this function for example
async function test(useError=false, args=[]) {
try {
// Some other code before promise chain below that could cause exception
if(useError) {
throw new Error(`Some error occured while processing ${args[0]}...`);
}
// await the promise and store the result in a variable
const promisedData = await Promise.resolve(`Promise delivered with ${args[0] ? args[0] : 'nothing'}!`);
// return the result (this will be a promise)
return promisedData;
} catch (err) {
// catch error that occurs within try block
console.log('==outer===', err);
}
}
// a simple generic async function runner for example
async function genericAsyncFunctionRunner(asyncFunction, ...args) {
let [useError, ...otherArgs] = args;
useError = useError ? true : false;
const result = await asyncFunction(useError, otherArgs);
// Output the result in console for example
console.log(result);
}
// run asyn function using the generic async function runner with/without arguments
genericAsyncFunctionRunner(test); // Promise delivered with nothing!
genericAsyncFunctionRunner(test, false, 'gratitude'); // Promise delivered with gratitude!
genericAsyncFunctionRunner(test, true, 'gratitude'); // ==outer=== Error: Some error occured while processing gratitude...

Getting UnhandledPromiseRejectionWarning despite several `try`-`catch` blocks

I'm using a 3rd party module that wraps around their API. I have the following code:
const api = require('3rdpartyapi');
async function callAPI(params) {
try {
let result = await api.call(params);
return result;
}
catch(err) {
throw err; //will handle in other function
}
}
async function doSomething() {
try {
//...do stuff
let result = await callAPI({a:2,b:7});
console.log(result);
}
catch(err) {
console.error('oh no!', err);
}
}
Despite both try-catch blocks, the 3rd party API, when it losses connection to homebase (happens quite frequently :( ), blows up with:
(node:13128) UnhandledPromiseRejectionWarning: FetchError: request to https://www.example.com failed, reason: getaddrinfo ENOTFOUND
Followed by:
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)
How come none of my try-catch catch this? What exactly is unhandled, and how to actually handle this?

The point is the await only converts "first layer" rejection into error, however the promise can have promise inside, and their library may fail to catch the rejection inside. I have made a proof of concept 3rdpartyapi which can trigger the behavior you see:
(async function () {
// mock 3rdpartyapi
var api = {
call: async function(){
await new Promise((resolve, reject) => {
// why wrap a promise here? but i don't know
new Promise((innerResolve, innerReject) => {
innerReject('very sad'); // unfortunately this inner promise fail
reject('this sadness can bubble up');
})
})
}
};
// your original code
async function callAPI(params) {
try {
let result = await api.call(params);
return result;
} catch (err) {
throw err; //will handle in other function
}
}
async function doSomething() {
try {
//...do stuff
let result = await callAPI({
a: 2,
b: 7
});
console.log(result);
} catch (err) {
console.error('oh no!', err);
}
}
doSomething();
})();
Output:
$ node start.js
oh no! this sadness can bubble up
(node:17688) UnhandledPromiseRejectionWarning: very sad
(node:17688) 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:17688) [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.

Calling a promise in a test get error 400 in NodeJS

I'm trying to use Contentful, a new JS library for building static websites. I want to use it in Node JS.
I created an app file like this (the name is getContent.js):
'use strict';
var contentful = require('contentful')
var client = contentful.createClient({
space: '****',
accessToken: '****'
});
module.exports = client;
function getEntry() {
return client.getEntry('******')
.then(function (entry) {
// logs the entry metadata
console.log(entry.sys)
// logs the field with ID title
console.log(entry.fields.channelName)
})
}
Then I created a test (getContent.test.js) like this:
'use strict';
let chai = require('chai');
let should = chai.should();
var expect = chai.expect;
var rewire = require("rewire");
let getContent = rewire("./getContent.js");
describe('Retreive existing', () => {
it('it should succeed', (done) => {
getContent.getEntry({contentName:'****'
}, undefined, (err, result) => {
try {
expect(err).to.not.exist;
expect(result).to.exist;
// res.body.sould be equal
done();
} catch (error) {
done(error);
}
});
});
});
but I obtain this error:
Retreive existing (node:42572) UnhandledPromiseRejectionWarning:
Error: Request failed with status code 400
at createError (/Users/ire/Projects/SZDEMUX_GDPR/api/node_modules/contentful/dist/contentful.node.js:886:15)
at settle (/Users/ire/Projects/SZDEMUX_GDPR/api/node_modules/contentful/dist/contentful.node.js:1049:12)
at IncomingMessage.handleStreamEnd (/Users/ire/Projects/SZDEMUX_GDPR/api/node_modules/contentful/dist/contentful.node.js:294:11)
at emitNone (events.js:111:20)
at IncomingMessage.emit (events.js:208:7)
at endReadableNT (_stream_readable.js:1064:12)
at _combinedTickCallback (internal/process/next_tick.js:138:11)
at process._tickCallback (internal/process/next_tick.js:180:9) (node:42572) 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: 3) (node:42572) [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.
Do you know what I'm missing? the promise is ok, I already tested it with a simple node getContent.js

I am seeing few issues with your code:
1. Invalid Args
In your test function, in getContent.js, you are passing an argument to the getEntry method (return client.getEntry('******'), whereas you are passing an object in the test (getContent.getEntry({}))
2. Mixing Promises & Callbacks
it('it should succeed', (done) => {
getContent.getEntry("****")
.then((result) => {
console.log(result);
try {
expect(result).to.exist;
// res.body.sould be equal
done();
} catch (error) {
done(error);
}
})
.catch(error => {
console.log(error);
done(error)
})
});
3. Source of Unhandled Promise rejection is not clear:
Is it coming from your test function in getContent.js, or, is it coming from your actual test?
Probably, this could also come from,
expect(err).to.not.exist;
expect(result).to.exist;
Always catch errors in Promises and reject it with proper reason to avoid issues like this.
Could you please update your code and repost it, so that its clear for other users?

Express route hanging async await

I am converting my application to use async/await instead of callbacks for query request made on the backend. It's been going good so far, but I am on a bit of a snag. My page is hanging on getting a get route and not rendering the ejs page. The console from the server also displays,
(node:7036)
UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): ReferenceError: qryFindLocalID is not defined
(node:7036) .
[DEP0018] DeprecationWarning: Unhandled promise rejections are depreca
ted. In the future, promise rejections that are not handled will terminate the Nod
e.js process with a non-zero exit code.
Any help would be appreciated.
The code so far is,
router.get("/secure", async (req, res) => {
let user = req.session.passport.user;
try {
if (user.chkUserStatus) {
if (user.lWaterLabID == 0 || user.lWaterlabID == -9999) {
// in both cases sLabID is set to 0
// assign the correct value for sLabName
user.sLabName = user.lWaterLabID == 0 ? "Site Admin" : "Uber Admin";
} else {
let labName = await request.query(
"Some Query"
);
user.sLabName = labName[0].sLabName;
}
} else {
// Houston we've got a problem ...
// user.chkUserStatus is not truthy
req.flash("loginMessage", "User Status is invalid.");
res.redirect("/");
}
const qryFindLocalID = await request.query(
`Some Query`
);
if (user.lWaterLabID == 0) {
const listRecentReports = await request.query(Some Query);
} else {
const listRecentReports = await request.query(Some Query);
}
} catch (err) {
// ... error checks
}
res.render("secure/index", {
qryFindLocalID: qryFindLocalID,
user: user,
listRecentReports: listRecentReports
});
});

The error message talks about an unhandled promise, but that's just wrapping the actual error, which is: ReferenceError: qryFindLocalID is not defined.
So where are you using qryFindLocalID? Ah, right at the bottom in the res.render call.
res.render("secure/index", {
qryFindLocalID: qryFindLocalID,
user: user,
listRecentReports: listRecentReports
});
Now why is qryFindLocalID undefined here? You defined it above in the try-catch block. But there's your problem -- You used const, so qryFindLocalID only exists in the try-catch. Outside of that, it doesn't exist.
You can fix that by using var in the try-catch (var is scoped to the function), or define qryFindLocalID using let ABOVE the try-catch.

Debug Unhandled Promise Rejections

I have written to following db query to get back all posts with a certain offset:
async function getPaginationPosts(start, size) {
try {
const posts = await knex("posts").select().where({
deleted: false,
}).orderBy("createdAt").limit(size).offset(start)
} catch (e) {
console.log(e.message)
console.log(e.stack)
}
return posts
}
However, I am getting the following Unhandled Promise Rejection
(node:1824) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): ReferenceError: posts is n
ot defined
(node:1824) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejection
s that are not handled will terminate the Node.js process with a non-zero exit code.
My problem is that I do not get any further information about the error in the console.
Any suggestions from your site:
How to debug these types of rejections properly?
What is wrong with the above code?
Thank you in advance for your replies!
Update
I changed my function to the following:
async function getPaginationPosts(size, offset) {
try {
return await knex("posts").select().where({
deleted: false,
}).orderBy("createdAt").limit(size).offset(offset)
} catch (e) {
console.log(e.message)
console.log(e.stack)
return null
}
}
Now I am getting the following exception:
(node:9096) UnhandledPromiseRejectionWarning: Unhandled promise rejection (rejection id: 1): ReferenceError: start is n
ot defined
I do not use a variable start in my function.
Any suggestions what I am doing wrong here?

A convenient way to log unhandled rejections - is to add listener (usually at entry point of your app, i.e. main.js) that looks like this
process.on("unhandledRejection", (error) => {
console.error(error); // This prints error with stack included (as for normal errors)
throw error; // Following best practices re-throw error and let the process exit with error code
});

posts are defined not in the correct place. Define them outside of try/catch block or return result from try block:
async function getPaginationPosts(start, size) {
try {
return await knex("posts").select().where({
deleted: false,
}).orderBy("createdAt").limit(size).offset(start)
} catch (e) {
console.log(e.message)
console.log(e.stack)
return null
}
}
Or:
async function getPaginationPosts(start, size) {
let posts
try {
posts = await knex("posts").select().where({
deleted: false,
}).orderBy("createdAt").limit(size).offset(start)
} catch (e) {
console.log(e.message)
console.log(e.stack)
}
return posts
}