Develop Reference

Javascript async/await return value is undefined, why?

I have a function that posts data via an API. I want to return the response...I am following tutorials online to try to understand async/await, and the way I have it laid out now seems to be correct to me.
I can print inside the postAsset.then statement, but the return value is always undefined. That's what I thought await fixed, unsure why it is still undefined in this case?
const postAsset = async (assetToPost) => {
let token = await retrieveToken()
if (token !== undefined && token !== 'Error') {
const config = {
headers: { Authorization: `Bearer ${token}` }
};
let urlAssets = `${API_ROUTE}${ASSETS.ASSETS_API_URL}`
axios
.post(urlAssets, assetToPost, config)
.then(function (response) {
let assetId = response.data
return assetId
})
.catch(function (error) {
console.log('POSTING ASSET ERROR: ', error.message);
return -1
})
}
}
const postData = async () => {
// post asset, get id response.
// then post beacons in loop, get id response for each
// then post a beaconId as part of assetId
let assetId = await postAsset(asset)
console.log(assetId)
}

Because you are using .then and not await - which would work if you'd return the promise that you get, but you don't.
Solution 1:
Return the promise you get from axios.post (add return in front of it):
return axios
.post(...)
.then(...)
Solution 2 (better):
Don't mix .then with async/await, instead only use async/await:
try {
const response = await axios.post(urlAssets, assetToPost, config)
return response.assetId
} catch (error) {
console.log('POSTING ASSET ERROR:', error)
return -1
}
(By the way, I changed error.message to just error so you won't lose the important stack information!)

the function postAsset should return a promise, and within the promise should execute the call axios.post

You're returning your assetId from the axios call but not returning anything from the postAsset method.
Just add the return keyword before you axios call. It will work.
return axios
.post(urlAssets, assetToPost, config)
.then(function (response) {
let assetId = response.data
return assetId
})
.catch(function (error) {
console.log('POSTING ASSET ERROR: ', error.message);
return -1
})

Mock a thrown exception

Is there a way to mock what a thrown exception in the try catch block? I want to test my function that the url string in error.message is indeed replaced with replacedURL string. How can I easily test it or mock the thrown exception to an object with this URL.
async function getUsers() {
try {
const response = await fetch('/api/users');
if (response.status >= 400) {
console.error('Could not fetch users');
return;
}
const users = response.json();
return users;
} catch (error) {
let message = error.message;
if (message) {
message = message.replace(/https:\/\/some.url.com /g, 'replacedURL');
delete error.message;
}
console.error('error', error);
}
}
Here's my test
test('url in error message is replaced', () => {
expect(getUsers()).toThrow('replacedURL');
})

You might want to actually throw an error in your function for it to be caught by toThrow.
Also, I'd recommend that your test doesn't actually tries fetching from the API (unless you're sure that's what you want it to do). Instead, consider using a custom caller (which can extend fetch) which you can then mock the response for, like const caller = jest.fn().mockRejectedValue({ message: 'https:://some.url.com' });

Multiple, dependent API calls in try/catch block? (NodeJS)

I am wondering how to best handle multiple, dependent API calls in nodejs with a try catch block. Say I need to send a request, wait for the response, then use the response in a subsequent API request to a different server and so on. I initially tried to separate these into several try/catch blocks, but then realised that if I am dependent on the response, I cannot really split subsequent requests apart.
Here is an example of what I mean:
try {
const token = await getAuth0Token();
const userExistsInAuth0 = await doesUserExist({
email,
token
});
if (!userExistsInAuth0) {
return res.status(500).json({
//...
});
}
// Create User
let createUserStatus = await createUser({
//....
});
if (createUserStatus == 'error') {
return res.status(200).json({
//...
});
}
const payment = await stripe.paymentIntents.create({
//...
});
return res.status(200).json({ //Success
//...
});
} catch (error) {
return res.status(500).json({ //Error
//...
});
}
Is this a recommended way to go about this? I am worried it will very soon get very messy, but I don't understand how I could break things apart.

You could define custom Error-classes and throw instances of these classes in your services. Then you handle those errors inside your already existing catch block. E.g:
class UserNotFound extends Error { ... }
class CreateUserError extends Error { ... }
// etc.
Then in your catch block you can use instanceof to determine the error:
try {
const token = await getAuth0Token();
// doesUserExist now throws an UserNotFound error if the user does not exist yet
const userExistsInAuth0 = await doesUserExist({
email,
token
});
// Create User
let createUserStatus = await createUser({
//....
});
const payment = await stripe.paymentIntents.create({
//...
});
return res.status(200).json({ //Success
//...
});
} catch (error) {
if (error instance of UserNotFound) { // handle UserNotFound error
} else if(error instance of CreateUserError) { // handle CreateUserError error
} else {
// handle any unhandled error
return res.status(500).json({ //Error
//...
});
}
}

Not able to catch exception from promise, error response is undefined

I've got some basic Javascript code that calls a stock API with symbols where the symbols are provided from a simple HTTP call like this:
GET http://localhost:4000/batch_stock_prices/?stocks=12312.
I believe I am misunderstanding the syntax for how to catch an exception from a promise..
An exception gets thrown that 12312 is an invalid symbol which I expect, on the terminal running the node server I see the exception but I'm not able to pass it back in the HTTP response. The error that's passed back in the response is 'undefined'. How can I catch the exception? Do I need a try catch somewhere?
const fetch = require('node-fetch')
const { IEXCloudClient } = require("node-iex-cloud");
const { type } = require('tap');
const iex = new IEXCloudClient(fetch, {
sandbox: true,
publishable: "pk_2f78524e5........23c327e24b5",
version: "stable"
});
'use strict'
async function getCurrentPriceOfBatchStocks(_stock) {
stocks_to_submit = _stock['stocks'];
console.log(stocks_to_submit)
response = await iex
.batchSymbols(stocks_to_submit)
.price()
.catch(function (error) { // <-- doesn't seem to get called
console.log("Exception: " + error);
throw error;
})
return new Promise((resolve, reject) => {
if (response) {
resolve(response)
} else {
reject(response); // <-- response is undefined. why?
}
});
}
const batchStocksSchema = {
querystring: {
type: 'object',
properties: {
stocks: {
type: 'string'
}
},
required: ['stocks']
}
}
module.exports = async function (fastify, opts) {
fastify.get('/batch_stock_prices/', {
schema: batchStocksSchema
}, async function (request, reply) {
try {
var response = await getCurrentPriceOfBatchStocks(request.query)
// console.log(response)
return reply
.code(200)
.send(response);
} catch (e) {
console.log(e)
return reply
.code(400)
.send('Bad Request, exception: ' + e) // outputs: ...exception: undefined
}
})
}

It's hard to say for sure what's wrong without running the code, but there are several issues with the use of async, await, and promises in the code, and with creating implicit globals. (Also various missing ;.) If we sort those out, it may be that whatever error is occurring will stop being obscured. See *** comments:
"use strict"; // *** This has to be at the very beginning of the compilation
// unit, it can't be later in the code as it is in the question
const fetch = require('node-fetch')
const { IEXCloudClient } = require("node-iex-cloud");
const { type } = require('tap');
const iex = new IEXCloudClient(fetch, {
sandbox: true,
publishable: "pk_2f78524e5........23c327e24b5",
version: "stable"
});
async function getCurrentPriceOfBatchStocks(_stock) {
// *** Declare `stocks_to_submit`
const stocks_to_submit = _stock['stocks'];
// *** Declare `response`
const response = await iex.batchSymbols(stocks_to_submit).price();
// *** Don't catch the error, let it propagate; the caller should
// know whether the call succeeded or failed
// *** Don't use `new Promise`, there's no purpose to it
return response;
}
const batchStocksSchema = {
querystring: {
type: 'object',
properties: {
stocks: {
type: 'string'
}
},
required: ['stocks']
}
};
// *** This function never uses `await`, so don't make it `async`
module.exports = function (fastify, opts) {
fastify.get('/batch_stock_prices/', {
schema: batchStocksSchema
}, function (request, reply) { // *** Typically old-style callback APIs don't do
// anything with the promise an `async` function
// returns, so don't pass `async` functions into them
getCurrentPriceOfBatchStocks(request.query)
.then(response => {
// *** No `return` here, we aren't resolving the promise from `then` with the result
// of `send`
reply
.code(200)
.send(response);
})
.catch(e => {
console.log(e);
// *** No `return` here, we aren't resolving the promise from `catch` with the
// result of `send`
reply
.code(400)
.send('Bad Request, exception: ' + e);
});
});
};

For why the catch is not called in this part:
response = await iex
.batchSymbols(stocks_to_submit)
.price()
.catch(function (error) { // <-- doesn't seem to get called
console.log("Exception: " + error);
throw error;
})
and why response is undefined:
return new Promise((resolve, reject) => {
if (response) {
resolve(response)
} else {
reject(response); // <-- response is undefined. why?
} });
This is the cause:
The promise returned by price() call had resolves an undefined value (instead of rejecting with an error). Your "await" wait for this undefined value and assigned it to "response" variable.
The price() when having problem have already handled the error and then print the details in the console:
Error: <html>
<head><title>400 Bad Request</title></head>
<body bgcolor="white">
<center><h1>400 Bad Request</h1></center>
<hr><center>nginx</center>
</body>
</html>
at IEXRequest.<anonymous> (/home/runner/ArtisticAridSite/node_modules/node-iex-cloud/lib/request.js:128:35)
at step (/home/runner/ArtisticAridSite/node_modules/node-iex-cloud/lib/request.js:32:23)
at Object.next (/home/runner/ArtisticAridSite/node_modules/node-iex-cloud/lib/request.js:13:53)
at fulfilled (/home/runner/ArtisticAridSite/node_modules/node-iex-cloud/lib/request.js:4:58)
It wasn't really passing the error back in the chain to your code.
So on your question of "How can I catch the exception?". Unfortunately you probably has no way to receive the exception details (unless you can control the error handling behaviour of iex). You may consider to check whether the result is undefined and handle accordingly.

this await throwing unexpected token error

I have a simple async function. It just sends a request and returns the data:
export const updatePanorama = async ({ commit }, payload) => {
const urlEnd = '/v1/pano/update'
const type = 'post'
const resp = await api.asyncRequest(urlEnd, type, payload)
commit('SET_PANORAMA', resp.data)
return resp
}
And this is how I'm using the function:
handleUpdatePanorama (panorama) {
const payload = {}
this.updatePanorama(payload).then(resp => {
this.setIsLoading(false)
this.handleAlert('updateSuccess', 'success')
}).catch(() => {
this.setIsLoading(false)
this.handleAlert('updateError', 'danger')
})
},
The problem is, the code after catch runs if there's an error inside then. But this way I don't know whether the catch error is an request error or and error triggered by the code inside then.
I'm trying try and catch to solve that problem:
handleUpdatePanorama (panorama) {
try {
const payload = {}
const resp = await this.updatePanorama(payload)
console.log('resp:', resp)
this.setIsLoading(false)
this.handleAlert('updateSuccess', 'success')
} catch (err) {
this.setIsLoading(false)
this.handleAlert('updateError', 'danger')
})
},
However, I get an unexpected token error in this line: await this.updatePanorama(payload)
What am I doing wrong?

The problem is, the code after catch runs if there's an error inside then
The solution for that is to not use catch, but the second then parameter. Have a look at the difference between .then(…).catch(…) and .then(…, …) for details.
I'm trying try and catch to solve that problem
That won't work, the catch clause will still be called if there's an exception thrown by setIsLoading or handleAlert.
I get an unexpected token error. What am I doing wrong?
You have not declared the handleUpdatePanorama method as async.
To mitigate the issues and fix the syntax, you could write
async handleUpdatePanorama (panorama) {
var result
try {
const payload = {}
const resp = await this.updatePanorama(payload)
console.log('resp:', resp)
result = ['updateSuccess', 'success']
} catch (err) {
result = ['updateError', 'danger']
} finally {
this.setIsLoading(false)
}
this.handleAlert(...result)
},

If you need to handle errors specifically from updatePanorama, use the second argument to .then(onSuccess, onError)
handleUpdatePanorama(panorama) {
const payload = {}
this.updatePanorama(payload).then(resp => {
this.setIsLoading(false)
this.handleAlert('updateSuccess', 'success')
}, err => {
// handle error from updatePanorama
// you can throw err if you also want to handle the error in .catch()
}).catch(() => {
this.setIsLoading(false)
this.handleAlert('updateError', 'danger')
})
}
note: if you return (or have no return statement) from the error handler, any subsequent .then(onSuccess will execute, if you throw an error (or return Promise.reject() for example, then the .catch() code will also run