class AuthController {
static methods = {
GET: {
'/auth/signup': {
func: AuthService.signUp,
response: (data, res) => {
res.statusCode = 200;
res.end(JSON.stringify(data));
},
},
},
};
static use(req, res) {
const route = this.methods[req.method][req.url];
if (!route) {
res.statusCode = 404;
res.end(JSON.stringify({ message: 'Not found 404!' }));
return;
}
try {
const data = JSON.parse(req?.body?.data || '{}');
const result = route.func({ ...data });
route.response(result, res);
} catch (err) {
console.log(err, 'here');
res.statusCode = err.statusCode || 500;
res.end(JSON.stringify(err.message));
}
}
}
class AuthService {
static async signUp({ login, password }) {
if (!login || !password) throw new BaseError(400, 'kl', 'Custom error');
}
}
It shows the error in console but try catch block doesn't see it.
Here is the traceback.
I don't know what the reason is because the function which throws error is inside of the block. Help please!
The trace back that you attached tells you exactly what the problem is and what you need to do:
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()
You can't catch an exception thrown by an async function with a try..catch block outside of that function, because script execution reaches the catch block before the async execution is finished. You therefor have to use .catch(..) instead:
const result = route.func({ ...data }).catch((err) => {
console.log("catched error: ", err);
});
I see one issue. You have declared signUp() to be async. That means it always returns a promise and it means that any throw operations inside it reject that promise that it returns (the exception doesn't propagate synchronously). But, when you attempt to call it here:
const result = route.func({ ...data });
You don't await it so when signUp() rejects, the promise goes into result, but nobody ever handles the fact that the promise rejected and you get UnhandlePromiseRejectionWarning from the system.
I can't see the whole overall design (of all the other routes), but perhaps you just need to add await to this:
const result = await route.func({ ...data });
And, you would have to make .use() be async also.
Or, if signUp() doesn't actually need to be async, then just remove the async from its declaration and the throw will be synchronous (instead of being turned into a rejected promise) and your try/catch will catch it then.
Related
I am struggling with some code... The 2 examples below I would think would work the same but the second example throws an error? I am also struggling to figure out the error, it's not bubbling up? Admittedly I am not a seasoned node developer so any guidance would be much appreciated! If it's relevant the create method in the module is calling the sequelize create.
This works
var p1 = deliverabiltyConfigs.create2(cfgObject);
return Promise.all([p1]).then(function([res1]) {
res.json({result: res1})
});
This does not
deliverabiltyConfigs.create2(cfgObject).then(res1 =>{
res.json({result: res1})
})
Here is the function that I am calling in a controller module
exports.create2 = (dConfig) => {
DeliverabilityConfig.create(dConfig)
.then(data => {
return data
})
.catch(err => {
return {
message:
err.message || "Some error occurred while createing this config."
};
});
};
The create2 function always returns null, so neither invocation will work. Promise.all([p1]) hides the problem, returning a promise to perform an array of no promises.
create2(cfgObject).then(res1 =>{ attempts to invoke then() on null, generating a more obvious error. But neither way works.
Fix by deciding which promise syntax you want, using each as follows:
Using original promise syntax....
exports.create2 = dConfig => {
// note the return
return DeliverabilityConfig.create(dConfig)
.catch(err => {
const message = err.message || "Some error occurred while createing this config.";
return { message };
});
};
// caller
deliverabiltyConfigs.create2(cfgObject).then(result =>{
res.json(result);
})
With recent syntactic sugar...
exports.create2 = async (dConfig) => {
try {
// its fine to not await here, since the caller will await
// but just to illustrate how you might perform more async work here...
return await DeliverabilityConfig.create(dConfig);
} catch (err) {
const message = err.message || "Some error occurred while createing this config."
return { message }
}
}
// caller
var result = await deliverabiltyConfigs.create2(cfgObject);
res.json(result);
Use Promise.all() to run >1 promise concurrently. You've only got one promise in the OP, so no reason for it here.
I have a function like this:
async getPatient(patientId: string): Promise<PatientDTO> {
const patient = await PatientDAO.getPatients({ id: patientId })
if (patient.length === 0) {
throw new NotFoundError("Patient Not Found!")
}
return patient[0]
}
But I got an error
UnhandledPromiseRejectionWarning: Error: Patient Not Found!
This happened cause I have used async function. How can I make this code running properly?
In order to manage errors in an async function, you have to use a try/catch block:
async getPatient(patientId: string): Promise<PatientDTO> {
try {
const patient = await PatientDAO.getPatients({ id: patientId })
return patient[0]
} catch (error) {
// Do whatever you may want with error
throw error;
}
}
I should mention, that if you simply want to throw the error thats received from getPatients theres no need for a try/catch block at all. Its only needed if you wish to modify the error or perform an extra action according to the error that was thrown.
You have 2 options:
First one is try/catch block with await keyword. Please notice that await has to be used in async function.
try {
const patient = await getPatient(foo);
// handle your data here
} catch(e) {
// error handling here
}
Second one is catch function
getPatient(foo)
.then(patient => {
// handle your data here
}).catch(error => {
// error handling here
});
I'm trying to test a failure mode of some mailing code which at the lowest level may throw an error. All the layers between the test and the function which throws are all async and use await on the functions below them. At the top level (also in an async function I have a try catch block. However node is throwing an unhandled promise exception before the error propages to this level.
My test code looks like this
beforeEach(function() {
//set default values - tests can change them
this.reasons = '';
this.reschedules = 0;
this.params.cid = 35124;
this.startTest = async () => {
/* this.confirmation is an async function under test,
this.mailer is a mock mailer with an async "send" method
which will throw an error in the correct test */
const doner = this.confirmation(this.mailer);
// ..other actions related to mocking database access made by confirmation
await doner;
return this.mailer.maildata; //provide info on parameters passed to this.mailer
};
});
it('Failure to send is reported', async function() {
this.mailer.sendResolve = false; //tell mock mailer to fail send request
try {
await this.startTest();
expect(true).to.be.false;
} catch(err) {
expect(err).to.be.instanceOf(Error);
}
});
the mock mailer is a bit like this
class Mailer {
constructor(user,params){
...
}
...
async send(subject, to, cc, bcc) {
this.maildata.subject = subject;
if (to !== undefined) this.maildata.to = to;
if (cc !== undefined) this.maildata.cc = cc;
if (bcc !== undefined) this.maildata.bcc = bcc;
if (!this.sendResolve) throw new Error('Test Error');
}
...
}
and a summary of the code under test
module.exports = async function(mailer) {
//get confirm data from database
const cData = await confirm(mailer.params.cid, mailer.db);
if (cData.count > 0) {
// ... format the email message and build it into maildata
await mailer.send(
subject,
emailAddress,
null,
process.env.PAS_MAIL_FROM,
{
pid:cData.pid,
type: 'confirmation',
extra: `Calendar ID ${mailer.params.cid} with procedure ${cData.procedure}`
}
);
debug('message sent, update the database');
await mailer.db.exec(async connection => {
...
});
debug('success');
} else {
debug('invalid calendarid');
throw new Error('Invalid Calendar ID');
}
};
As can be seen the call path from the async send function which throws back up the stack to the try {}catch(){} are all async functions. But when I run this test node outputs an unhandled promise rejection.
I've tried using the visual studio code debugger to single step through this, I get a bit lost caught in the machinery which wraps async functions to turn them into promises providers. As far as I can see, one layer of error is handled correctly and then fails at the next layer up.
Does this mean that every async function must have a try catch block to catch and rethrow any error? I can't find any explanation that says I have to do that.
To answer your question:
Does this mean that every async function must have a try catch block to catch and rethrow any error?
Errors propogate up through await-ed calls like you expected:
const assert = require('assert');
const outer = async () => {
await middle();
}
const middle = async () => {
await inner();
}
const inner = async () => {
throw new Error('something bad happened');
}
it('should catch the error', async () => {
let errorMessage;
try {
await outer();
}
catch (err) {
errorMessage = err.message;
}
assert(errorMessage === 'something bad happened'); // Success!
});
...so no, you don't need a try / catch block at every level.
Tracking down unhandled Promise rejections
I can't see exactly where the await chain might be broken in the code from your sample, but to help track down unhandled Promise rejections you can add a process handler for the unhandledRejection event and look at the logged Promise to see where the rejection began and track backwards through the call stack from there:
const assert = require('assert');
const outer = async () => {
await middle();
}
const middle = async () => {
inner(); // <= this will cause an Unhandled Rejection
}
const inner = async () => {
throw new Error('something bad happened');
}
it('should catch the error', async () => {
let errorMessage;
try {
await outer();
}
catch (err) {
errorMessage = err.message;
}
assert(errorMessage === undefined); // Success! (broken await chain)
})
process.on('unhandledRejection', (reason, p) => {
console.log('Unhandled Rejection at:', p);
console.log('reason:', reason);
});
...which in this case logs:
Unhandled Rejection at: Promise {
<rejected> Error: something bad happened
at inner (.../code.test.js:12:9)
at inner (.../code.test.js:8:3)
at middle (.../code.test.js:4:9) // <= this is the broken link
at Context.outer (.../code.test.js:18:11)
at callFn (...\node_modules\mocha\lib\runnable.js:387:21)
...
...which points us to the Error thrown in inner, and by tracing up the chain we find middle to be the broken link.
const fetch = require('node-fetch');
let url = 'something.com';
module.exports = function(context) {
let a = fetch(url)
a.then(res => {
if(res.status!=200) throw new Error(res.statusText)
else{
context.done(null, res.body);
}
});
a.catch(err => {
console.log(err)
throw new Error(err)
});
};
I have a durable function that calls an activity function like above. I have set automatic retry on failure on this activity function. To retry the function needs to get an error.
So In get request I want to throw an error when i get response like 404 or something similar. But when i throw from catch block i get an error like below
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().
function pauses there and stops execution.I have to manually stop and start the execution. How can i handle this so that the function retries?
Your code branches.
Ignoring the detail, what you have is :
let a = <Promise>; // root
a.then(...); // branch_1
a.catch(...); // branch_2
So whereas you catch errors arising in a, any error arising in branch 1 will be uncaught. Hence the warning
Compare that with :
let a = <Promise>; // root
a.then(...).catch(...); // branch
or
<Promise>.then(...).catch(...); // no assignment necessary
So, you might write :
module.exports = function(context) {
return fetch(url)
.then(res => {
if(res.status!=200) {
throw new Error(res.statusText);
} else {
context.done(null, res.body);
}
})
.catch(err => {
console.log(err)
throw new Error(err)
});
};
Alternatively, depending on the required division of responsibilities between module and caller(s) ...
module.exports = function(context) {
return fetch(url)
.then(res => {
if(res.status!=200) {
throw new Error(res.statusText);
} else {
return res;
}
});
};
... and call .context.done(null, res.body); in a .then() callback in the caller.
In both cases, with return included, then the caller will need to catch errors otherwise you will again get an unhandled error warning.
Found that with the use of async/await this problem goes away and the function re-try after exception is thrown.
const fetch = require('node-fetch');
let url = 'something.com';
module.exports = async function(context) {
let res = await fetch(url)
if(res.status!=200) throw new Error(res.statusText);
else return res.body;
};
For example,
Comments.findOne({user: req.user.id}).exce()
.then(function(comment) {
if(comment) {
// how to make this return immediately and break the rest then?
return res.json({error: 'Already commented'});
} else {
return Posts.findOne({postId: req.params.id}).exec();
}
})
.then(function(post) {
if(post) {
var comment = new Comment({user: req.user.id, data: req.body.comment})
return {post: post, comment: comment.save()};
} else {
return res.json({error: 'Post not exist'});
}
})
.then(function(data) {
post.comments.push(comment._id);
return post.save();
});
.then(function(post) {
return res.json({ok: 1})
})
.catch(function(e)) {
return res.json(error: e);
});
Is this promise written right?
How to write this kind of promise?
Callbacks/Promises is a headache...
You're using bluebird, it supports cancellation. Here's an example:
var Promise = require('bluebird');
// enable cancellation
Promise.config({
cancellation: true
});
// store your promise chain
var myPromise = Promise.resolve().then(() => {
return 'foo';
}).then((res) => {
console.log(res);
// call cancel on the chain when needed
myPromise.cancel();
return res;
}).then((res) => {
// this will not be executed
console.log(res + '2');
});
You just need to throw or return a reject promise to trigger the error handling in promises as show in this example:
Comments.findOne({user: req.user.id}).exce()
.then(function(comment) {
if(comment) {
// to bypass all the other .then() resolve handlers, either
// throw an error here or return a rejected promise
throw new Error(res.json({error: 'Already commented'}));
} else {
return Posts.findOne({postId: req.params.id}).exec();
}
})
Promises are "throw safe" which means that .then() will catch any exception thrown and turn it into a rejected promise. This will bypass any following .then() resolve handlers and will instead go to the next reject handler or .catch() handler.
FYI, you should be careful in your code because when you .catch() and then just return from that, it changes your promise state from rejected to resolved and it will then look like a successful promise when you actually had an error and any caller will think everything was successful. This is because the promise infrastructure assumes that if you .catch() an error and return a value that you have "handled" the error and the state is now resolved successfully. To allow the error to continue to propagate to higher callers from a .catch(), you have to re throw or return a rejected promise:
blah(...).then(...)
.catch(function(e)) {
throw new Error(res.json(error: e));
});