Develop Reference

Why re-throwing error in catch block having TypeError

I have a route handler in express.js and inside it, I am calling an asynchronous function which should return me some value. I am using bluebird promises to handle the promises. Below is a sample code.
router.js
---------
router.post('/endpoint', (req, res) => {
return Promise.try(() => serviceFile.validate())
.then(() => {
console.log('Response: ', response);
})
.catch((error) => {
console.log('Error: ', error) // TypeError: expecting a function but got [object Promise]
})
})
serviceFile.js
--------------
async function validate() {
return Promise.try(() => axios.post('/endpoint'))
.then((response) => response.data)
.catch((error) => {
console.log('Error: ', error.response.data) // successfully printing the error data object
throw error;
})
}
When I call the validate() in the Service.js file, it fails the request (which I want) and successfully prints the error. But I don't want to handle the error here, so I re-throw it and expects to handle it in the router.js file. But in the router.js file, I am getting error as undefined and it says, TypeError: expecting a function but got [object Promise]
I am not getting any clue where I am doing wrong. Any help would be greatly appreciated.

its sort of unclear what serviceFile.validate does unless thats the second function you listed, this might be a more clear way of using promises
router.post('/endpoint', async (req, res) => {
try {
const response = await serviceFile.validate()
console.log('Response: ', response);
} catch (err) {
console.log('Error: ', error)
}
})
function validate () {
return new Promise(async (resolve, reject) => {
try {
const res = await axios.post('/endpoint')
resolve(res.data)
} catch (err) {
if (err.response && err.response.data) {
reject(err.response.data)
} else {
reject(err)
}
}
})
}

catching exception thrown by service worker message event

I can't catch an exception thrown by the service worker's message event..
The client uses following code to execute the command on the SW:
import { messageSW } from "workbox-window";
// .. code for Workbox initialization/registration omitted
messageSW(registration?.active, { type: "SYNC" })
.then((results) => {
console.log("done");
})
.catch((e) => {
console.error(e);
});
On the SW (sw.js) side I have the following code:
self.addEventListener("message", async (event) => {
if (requestType === "SYNC") {
event.ports[0].postMessage(await longRunningTask());
}
});
This solution works OK as long as the SW is not throwing any exceptions. Meaning that the client prints the "done" message after the long running process on the SW is executed. If the exception is thrown nothing gets returned, ever.
I have managed to fix the problem by doing the following:
self.addEventListener("message", async (event) => {
if (requestType === "SYNC") {
try {
event.ports[0].postMessage(await longRunningTask());
} catch (error) {
event.ports[0].postMessage(error);
}
}
});
In this case - the result is always returned regardless, "done" is printed, but:
how do I actually produce an exception from the service worker, so the client could catch and handle it?
In general it would be good to hear if what I am doing is an appropriate approach to how asynchronous code on the SW shall be invoked from the client...

Here is my own solution I ended up using:
On service worker side - helper method:
async function replyToSenderAsync(event, task) {
let isCanReply = event.ports && event.ports.length >= 0;
try {
const result = await task();
if (isCanReply) {
event.ports[0].postMessage({ error: null, message: result });
}
} catch (error) {
if (isCanReply) {
event.ports[0].postMessage({ error: error, message: null });
}
}
}
When exception is caught we set the error property. Use as:
self.addEventListener("message", async (event) => {
const requestType = event?.data?.type;
if (requestType === "QUEUE_CLEAR") {
await replyToSenderAsync(event, async () => await clearQueueAsync());
}
});
On client side request wrapper:
function sendMessageToSWAsync(targetSW, messageType, message) {
return new Promise(function (resolve, reject) {
if (
!isServiceWorkerSupported.value ||
!isServiceWorkerRegistered.value ||
!targetSW
) {
reject(new Error("Unable to send the message to a service worker"));
}
try {
messageSW(targetSW, { type: messageType, message: message })
.then((messageResponse) => {
if (!messageResponse) {
reject(new Error("Service worker responsed with empty response"));
} else {
if (messageResponse.error) {
reject(messageResponse.error);
} else {
resolve(messageResponse.message);
}
}
})
.catch((messageError) => {
reject(messageError);
});
} catch (error) {
reject(error);
}
});
}
The magic here is to read the error property and reject the promise if that is the case (hence causing an exception to be thrown). Use as
try {
let response = await sendMessageToSWAsync(registration?.active, "QUEUE_GET_ALL");
}
catch(error) {
}
sendMessageToSWAsync(registration?.active, "QUEUE_GET_ALL")
.then((response) => {})
.catch((error) => {})

How to handle errors with Async and Await [Node.js]

I have already a function written with bluebird promises and I would like to rewrite it with async and await. When I have made the changes I have found out that earlier with promises the reject statement always transfers the control to called function catch block though if the catch block is already there in the file from where we are rejecting. How to handle this situation properly with async and await?. (Added comments to the code to explain the issue)
With Promise:
const callingFunc = (req, res) => {
return new Promise((resolve, reject) => {
// execute request which returns promise
functionCall()
.then((response) => {
let error;
try {
xml2js(response.body, { explicitArray: false }, (err, result) => {
if (err) {
return reject(err); /* throws the correct error to catch block of the file from where callingFunc is called*/
}
if (!_.isEmpty(result.Response.errorCode)) {
return reject(result.Response); /* throws the correct error to the catch block of the file from where callingFunc is called*/
}
return resolve(result);
});
} catch (e) {
error = new Error('xml2js conversion error');
reject(error);
}
})
.catch((error) => {
const Error = new Error('Internal Server Error');
reject(Error);
});
});
};
With async and await:
const callingFunc = (req, res) => {
try {
const response = await functionCall();
let error;
try {
xml2js(response.body, { explicitArray: false }, (err, result) => {
if (err) {
throw (err); /* throws the error to the below catch block and returning xml2js conversion error and changing behaviour*/
}
if (!_.isEmpty(result.Response.errorCode)) {
throw result.Response; /* throws the error to the below catch block and returning xml2js conversion error and changing behaviour*/
}
return result;
});
} catch (e) {
error = new Error('xml2js conversion error');
throw error;
}
} catch(error) {
const Error = new Error('Internal Server Error');
throw Error;
}
};

If functionCall returns a promise, then this code is inappropriate...
return new Promise((resolve, reject) => {
// execute request which returns promise
functionCall()
.then((response) => {
If xml2js is async using callbacks, then it is appropriate to wrap it in a promise...
// return a promise that resolves with the result of xml2js
async function xml2js_promise(body) {
return new Promise((resolve, reject) => {
xml2js(body, { explicitArray: false }, (err, result) => {
if (err) reject(err);
else if (!_.isEmpty(result.Response.errorCode)) reject(result.Response);
else resolve(result);
});
});
}
Now we can await these. There's no need to nest the try's. (And you only need the try if you're going to do something on the catch).
async callingFunction = (req, res) => {
try {
const response = await functionCall();
} catch (error) {
// do something with this error
}
try {
const result = await xml2js_promise(response.body)
} catch(error) {
// do something with this error
}
return result;
}

How to handle API response errors in async/await

I'm trying to better understand error handling while using async/await, third party libs, and external APIs.
Given the following pseudo-code:
const createConnectionRequest = async (args) => {
try {
const { data } = axios.post(url, args);
return data;
} catch (err) {
throw new Error(err);
}
}
My understanding is the throw would occur a result of the axios.post failing rather than an issue with my request.
If the response from my API was 200 but included an error of some sort, eg.
{
status: 200,
error: 'Invalid fields supplied',
}
Would I throw this error in the try block and expect a parent calling function to catch it?
const createConnectionRequest = async (args) => {
try {
const { data } = axios.post(url, args);
if (data.error) {
throw new Error(data.error);
}
return data;
} catch (err) {
throw new Error(err);
}
}
...
const processor = async () => {
try {
await createConnectionRequest(...);
} catch (err) {
// handle error from API response here
throw new Error(err);
}
}

Use try/catch on method

I use multiple same try/catch test on many object method. So, i would like create try/catch method for refacto my code, but the error is not returned.
For exemple :
#autobind
async forgottenPassword(req, res) {
return this.callService(
res,
async () => await companyService.forgottenPassword(req.body.formData)
);
}
callService(res, func) {
try {
func();
} catch (error) {
res.statusMessage = error.message;
res.status(error.statusCode);
} finally {
res.end();
}
}
My catch is never called :/
Anyone know did I make a mistake ?
Thank you !

You need to make your callService async and use await there too.
#autobind
async forgottenPassword(req, res) {
return this.callService(
res,
async () => await companyService.forgottenPassword(req.body.formData)
);
}
async callService(res, func) {
try {
await func();
} catch (error) {
res.statusMessage = error.message;
res.status(error.statusCode);
} finally {
res.end();
}
}