I am implementing a cloud function for signing up with unique username and password.
In order to throw exceptions, I was previously doing the following:
signUpValidation.js
if (!validateUsername(username)) {
throw new functions.https.HttpsError(
"invalid-argument",
"Invalid username.",
{
status: "error",
code: "auth/invalid-username",
message: "Username must be between 3 and 30 characters, including numbers, letters, hyphens, periods, or underscores.",
}
);
}
signUp.function.js
try {
await validateSignUpData(
username,
email,
password,
repeatPassword,
name,
birthday,
clientIp
);
} catch(err) {
if (err instanceof functions.https.HttpsError) {
throw err;
}
// An unknown error has occurred
console.error(err);
throw new functions.https.HttpsError(
"unknown",
"Unexpected error.",
{
status: "error",
code: err.code ?? "unknown",
message: err.message ?? "The registration request could not be processed. Please, try again later."
}
);
}
But, I don't really like this way of throwing the exceptions in the signUpValidation module... it makes more sense to me to throw "AuthErrors" instead of "HttpsErrors".
So, as it seems not possible to extend the default Firebase Errors, I have decided to create my own util/authErrors module:
class AuthError extends Error {
constructor(code, message) {
super(message);
this.code = code;
this.name = "AuthError";
}
}
const authErrors = Object.freeze({
usernameAlreadyExists(message = "The username is already in use by an existing account") {
return new AuthError('auth/email-already-exists', message);
}
... more errors
});
module.exports = authErrors;
as you can see, I have created my custom Error and some factory functions for every error type. Then, in my signUpValidation.js, I just do:
if (!(await isUsernameUnique(username))) {
throw authErrors.usernameAlreadyExists();
}
Is it possible to extend a FirebaseError? If not, why?
Is it considered a bad practice to work this way in order to throw custom exceptions in Cloud Functions? I mean, should I just throw HttpsErrors?
Having Custom Error Type is useful if you are going to treat it differently.
For example if you have a try/catch block and want to have a different logic for your custom error.
but here you are passing error to client which has no idea of either Firebase HttpsError or your custom AuthError. because at the end your object will be serialized to JSON and at the other end there is no class to convert it back to HttpsError or AuthError.
Also at HTTP protocol level, authentication errors are defined by HTTP status codes (e.g. 401 ,403) so they are not inherently different object types.
What I'm saying is that I don't see any advantage in having a custom AuthError class on your server side when it can not be transformed as it is to your client to be treated differently.
For client the HTTP status code is the key to differentiate an Auth error from other type of errors.
Could some one help me out on below question please :-)
I'm making a post call through redux action, which is below.
export const addEmployee = ({ firstName, surname, contactNumber, email }) => async dispatch => {
const payloadBody = JSON.stringify({ firstName, surname, contactNumber, email });
fetch('/api/users', {
method: 'POST',
body: payloadBody,
headers: {
'Content-Type': 'application/json'
}
})
.then(response => {
if (!response.ok) {
return response.text()
.then(text => {
throw Error(text)
});
} else {
dispatch(setAlert("New Employee added ", 'danger'));
}
})
.catch(error => {
console.log('>>> in CATCH block, error is =>', error);
console.log('>>> in CATCH block, error name is =>', error.name);
console.log('>>> in CATCH block, error message is =>', error.message);
let allKeys = Object.getOwnPropertyNames(error);
console.log(allKeys);
// const errors = [];
// Object.keys(error.message).forEach(key => {
// console.log('>>> key are ', key)
// })
// const keys = Object.keys(error.message);
// console.log(keys);
// const errors = error.message['errors'];
// const errors = error.response.data.errors;
// if (errors) {
// errors.forEach(error => dispatch(setAlert(error.msg, 'danger')));
// }
dispatch({
type: REGISTER_FAIL
});
})
}
Above post call on failure, returns body with error message, an example is below
{
"errors": [
{
"msg": "User already exist with email"
}
]
}
Question
What I'm trying to achieve is, to grab the errors[] and pass the error message through to a component, the trouble I have is accessing the error[] array within the returned array message. I'll describe below what I've attempted, it also can be seen in the redux action method I posted above.
Try-1
console.log('>>> in CATCH block, error is =>', error); yields just Error
Try-2
console.log('>>> in CATCH block, error name is =>', error.name); yields {"errors":[{"msg":"User already exist with email"}]} and the typeof this is string since I'm returning text() return response.text().then(text => { throw Error(text) })
Try-3
When I return as json() return response.json().then(text => { throw Error(text) })and console.log('>>> in CATCH block, error message is =>', error.message); yields object.
The questions again What I'm trying to achieve is, to grab the errors[] and pass the error message through to a component such as below
const errors = error.message; // this is where I'd like to extract the error.
if (errors) {
errors.forEach(error => dispatch(setAlert(error.msg, 'danger')));
}
Hope the above description is clear, please let me know if you require more info,
I know I'm missing some crucial knowledge of working with error objects, could someone please shed some light on this please :-)
Pattern for throwing errors recovered from standard-format HTTP payload
Your redux action does work over HTTP. Sometimes the server responds with bad news, and it seems like there's a standardized format the server uses to report that news. Also, sometimes your own code throws. You want to handle both kinds of problem with control structures related to Errors.
Basic pattern for an async Redux action
Before we start: your action is marked async, but you're still chaining .then and .catch. Let's switch to async/await, converting this:
export const addEmployee = (/*...*/) = async ( dispatch, getState ) => {
fetch(/* ... */)
.then(response => {
return response.text()
.then(text => {
// happy-path logic
throw Error(text)
})
})
.catch(error => {
// sad-path logic
dispatch(/* ... */)
})
}
...into this:
export const addEmployee = (/*...*/) = async ( dispatch, getState ) => {
try {
let response = await fetch(/* ... */)
let responseText = await response.text()
// happy-path logic
dispatch(/* ... */)
return // a redux action should return something meaningful
} catch ( error ) {
// sad-path logic
dispatch(/* ... */)
return // a failed redux action should also return something meaningful
}
}
Now let's talk about errors.
Error basics
Meet throw:
try { throw 'mud' } catch( exception ) { /* exception === 'mud' */ }
try { throw 5 } catch( exception ) { /* exception === 5 */ }
try { throw new Date() } catch( exception ) { /* exception is a Date */ }
You can throw just about anything. When you do, execution halts and immediately jumps to the closest catch, searching all the way through the stack until it finds one or runs out of stack. Wherever it lands, the value you provided to throw becomes the argument received by catch (known as an "exception"). If nothing catches it, your JS console logs it as an "uncaught exception."
You can throw anything, but what should you throw? I think you should only throw instances of Error, or one of its subclasses. The two main reasons are that the Error class does some helpful things (like capturing a stacktrace), and because one of your two sources of failure is already going to be throwing Error instances, so you must do something similar if you wish to handle both with a single codepath.
Meet Error:
try {
throw new Error('bad news')
} catch ( error ) {
console.log(error.message)
//> 'bad news'
}
We already know that an Error will be thrown if code within your action blows up, e.g. JSON.parse fails on the response body, So we don't have to do anything special to direct execution onto the catch path in those scenarios.
The only thing we have to be responsible for is to check whether the HTTP response contains something that looks like your server's "standard error payload" (more on that later), which your sample suggests is this:
{
"errors": [
{
"msg": "ERROR CONTENT HERE"
}
]
}
Here's the core issue
This handling has to be special because no javascript engine considers it an error simply to receive an HTTP payload that can be parsed as JSON and which contains a key named "errors". (Nor should they.) This payload pattern is merely a custom convention used by some or all of the HTTP endpoints that you talk to.
That's not to say it's a bad idea. (I think it's great!) But that explains why it must be done custom: because this pattern is just your private little thing, and not actually special in a way that would make browsers treat it the special way you want.
So here's our plan:
make the request, relying on try/catch to capture things thrown by our tools
if we get a response that seems bad:
examine the payload for an error encoded in the "standard format"; I call anything like this an "API error"
if we find an API error, we will create and throw our own Error, using the API error content as its message
if we don't find an API error, we'll treat the raw body text of the response as the error message
if we get a response that seems good:
dispatch the good news (and useful data) to the store
Here's what that looks like in code:
export const addEmployee = ({
firstName,
surname,
contactNumber,
email
}) => async ( dispatch, getState ) => {
const payloadBody = {
firstName,
surname,
contactNumber,
email
}
try {
// step 1
let response = await fetch('/api/users', {
method: 'POST',
headers: { 'Content-Type': 'application/json' },
body: JSON.stringify(payloadBody)
})
let responseText = await response.text()
if (!response.ok) {
// step 2
let errorString = getErrorMessageFromResponseBody(responseText)
throw new Error(errorString) // API errors get thrown here
}
// step 3
let responseJson = JSON.parse(responseText)
dispatch(setAlert('New Employee added', responseJson.user.name))
/*
A redux action should always returns something useful.
addEmployee might return the `user` object that was created.
*/
return responseJson.user
} catch ( error ) {
// all errors land here
dispatch({
type: REGISTER_FAIL,
message: error.message
})
/*
A failed redux action should always return something useful (unless you prefer to throw).
For now, we'll return the reason for the failure.
*/
return error.message
}
}
function getErrorMessageFromResponseBody( string ) {
let errorString = string
try {
let json = JSON.parse(string)
if(json.errors) {
errorString = json.errors[0].msg
}
} catch ( parseOrAccessError ) {}
return errorString
}
Here's what can be thrown to that catch block:
anything thrown by JSON.parse when applied to the arguments
anything thrown by fetch
if !response.ok, the whole response payload (or just an error message if the payload contains an API error)
Exception handling
How can you tell those different kinds of failure apart? Two ways:
Some failures throw specific subclasses of Error, which you can test for with error instanceof SomeErrorClass:
JSON.stringify throws a TypeError if it can't serialize its argument (if you have custom .toJSON anywhere, it can also throw anything that throws)
fetch throws a TypeError if it can't reach the internet
JSON.parse throws a SyntaxError if the string can't be parsed (if you use a custom reviver, those errors get thrown too)
Any instance of Error or its subclasses will have a .message; you can test that string for specific cases
How should you handle them?
If JSON.stringify blows up, it's because you wired your data wrong. In that case, you probably want to do something that will alert the developer that something is broken and help diagnose the issue:
console.error(error)
dispatch some failure action that includes the error.message
show a generic error message on-screen
If fetch throws, you could dispatch a failure that presents a "fix your wifi" warning to the user.
If JSON.parse throws, the server is melting down, and you should show a generic error message.
A little sophistication
Those are the basic mechanics, but now you confront a messy situation. Let's list some challenges:
You may have already noticed one problem: "no internet" will present the same way as "circular data": a thrown TypeError.
It turns out that the precise text of JSON.stringify errors depends on the actual value supplied to that function, so you can't do something like error.message === CONSTANT_STRINGIFY_ERROR_MESSAGE.
You may not have an exhaustive list of every msg value the server can send in an API error.
So how are you supposed to tell the difference between a problem reported by a sane server vs a client-side bug vs a broken server vs unusable user data?
First, I recommend creating a special class for API errors. This lets us detect server-reported problems in a reliable way. And it provides a decent place for the logic inside getErrorMessageFromResponseBody.
class APIError extends Error {}
APIError.fromResponseText = function ( responseText ) {
// TODO: paste entire impl of getErrorMessageFromResponseBody
let message = getErrorMessageFromResponseBody(responseText)
return new APIError(message)
}
Then, we can do:
// throwing
if (!response.ok) {
// step 2
throw APIError.fromResponseText(responseText)
}
// detecting
catch ( exception ) {
if(exception instanceof APIError) {
switch(APIError.message) {
case 'User already exist with email':
// special logic
break
case 'etc':
// ...
}
}
}
Second, when throwing your own errors, never provide a dynamic string as the message.
Error messages for sane people
Consider:
function add( x, y ) {
if(typeof x !== 'number')
throw new Error(x + ' is not a number')
if(typeof y !== 'number')
throw new Error(y + ' is not a number')
return x + y
}
Every time add is called with a different non-numeric x, the error.message will be different:
add('a', 1)
//> 'a is not a number'
add({ species: 'dog', name: 'Fido' }, 1)
//> '[object Object] is not a number'
The problem in both cases is that I've provided an unacceptable value for x, but the messages are different. That makes it unnecessarily hard to group those cases together at runtime. My example even makes it impossible to tell whether it's x or y that offends!
These troubles apply pretty generally to the errors you'll receive from native and library code. My advice is to not repeat them in your own code if you can avoid it.
The simplest remedy I've found is just to always use static strings for error messages, and put some thought into establishing conventions for yourself. Here's what I do.
There are generally two kinds of errors:
some value I wish to use is objectionable
some operation I attempted has failed
In the first case, the relevant info is:
which datapoint is bad; I call this the "topic"
why it is bad, in one word; I call this the "objection"
All error messages related to objectionable values ought to include both datapoints, and in a manner that is consistent enough to facilitate flow-control while remaining understandable by a human. And ideally you should be able to grep the codebase for the literal message to find every place that can throw the error (this helps enormously with maintenance).
Here is how I construct the messages:
[objection] [topic]
There is usually a discrete set of objections:
missing: value was not supplied
unknown: could not find value in DB & other "bad key" issues
unavailable: value is already taken (e.g. username)
forbidden: sometimes specific values are off-limits despite being otherwise fine (e.g. no user may have username "root")
invalid: heavily overused by dev community; treat as option of last resort; reserved exclusively for values that are of the wrong datatype or syntactically unacceptable (e.g. zipCode = '__!!#')
I supplement individual apps with more specialized objections as needed, but this set comes up in just about everything.
The topic is almost always the literal variable name as it appears within the code block that threw. To assist with debugging, I think it is very important not to transform the variable name in any way.
This system yields error messages like these:
'missing lastName'
'unknown userId'
'unavailable player_color'
'forbidden emailAddress'
'invalid x'
In the second case, for failed operations, there's usually just one datapoint: the name of the operation (plus the fact that it failed). I use this format:
[operation] failed
As a rule, operation is the routine exactly as invoked:
try {
await API.updateUserProfile(newData)
} catch( error ) {
// can fail if service is down
if(error instanceof TypeError)
throw new Error('API.updateUserProfile failed')
}
This isn't the only way to keep your errors straight, but this set of conventions does make it easy to write new error code without having to think very hard, react intelligently to exceptions, and locate the sources of most errors that can be thrown.
Handling server inconsistencies
A final topic: it's pretty common for a server to be inconsistent about how it structures its payloads, particularly with errors but also with successes.
Very often, two endpoints will encode their errors using slightly different envelopes. Sometimes a single endpoint will use different envelopes for different failure cases. This is not usually deliberate, but it is often a reality.
You should coerce all the different flavors of server complaint into a single interface before any of this madness can leak into the rest of your application, and the shore of the client/server boundary is the best place to immediatley jettison server weirdness. If you let that stuff escape into the rest of your app, not only will it drive you insane, but it will make you brittle by allowing the server to surface errors deep inside your app, far away from the real source: a violated API contract.
A way to support a variety of envelopes is by adding extra code to getErrorMessageFromResponseBody for each of the different envelopes:
function getErrorMessageFromResponseBody( string ) {
let errorString = string
/*
"Format A"
{ errors: [{ msg: 'MESSAGE' }] }
used by most endpoints
*/
try { /*... */ } catch ( parseOrAccessError ) {}
/*
"Format B"
{ error: { message: 'MESSAGE' } }
used by legacy TPS endpoint
*/
try { /*... */ } catch ( parseOrAccessError ) {}
/*
"Format C"
{ e: CODE }
used by bandwidth-limited vendor X
use lookup table to convert CODE to a readable string
*/
try { /*... */ } catch ( parseOrAccessError ) {}
return errorString
}
One of the values of having a dedicated APIError class to wrap these things is that the class constructor provides a natural way to gather all this up.
Because the discord doesn't support to delete messages older than 14 days. I want to create an exception to the error, when the bot is trying to delete old messages,but the throw in .catch doesn't work and i don't know why.
This is my code:
try{
message.channel.bulkDelete(200, false)
.catch(error =>{
throw 1;
});
message.channel.send(“Deleted 200 messages”);
}catch(error){
message.channel.send(“cant delete messages”);
}
I know that i can do this bulkDelete(200, true) but that wont throw exception when it is trying to delete the old messages.
Try to do this
try {
await message.channel.bulkDelete(100, false);
message.channel.send("Deleted 100 messages");
} catch(error) {
message.channel.send("Can't delete messages");
}
bulkDelete is a promise so you have to put it in an async function and await it or use the .then syntax. Also it can delete only 100 messages and returns an error with more.
I'm not sure why you want to throw 1 when you get an error but if you need it you can put it in the catch statement after sending the message
I'm a beginner in Node/Express.js and I'm trying out some try catch logic but doesn't seem to work as expected.
app.get("/tasks/:id", async (req, res) => {
try {
const _id = req.params.id;
const task = await Task.findById(_id);
if (!task) {
return res.status(404).send("task not found");
}
res.send(task);
} catch (error) {
res.status(500).send("Internal server error");
}
});
from this code sample, I'm making a query to Mongo DB to fetch some task but the problem is that if the task is not found, instead of running through the if statement, the program jumps directly to the catch block hence the if condition is not checked thus resulting to a different error. How can I fix this issue?
This is simply how MongooseJS works - check their Promises documentation and you will see that if a document is not found, an error will be thrown. If you were not using await, the findById() documentation shows how an error is returned if it cannot be found:
// find adventure by id and execute
Adventure.findById(id, function (err, adventure) {});
You can simply modify your route to look like the following:
app.get("/tasks/:id", async (req, res) => {
let task;
try {
task = await Task.findById(req.params.id);
} catch (error) {
return res.status(404).send("task not found");
}
/* perform other checks or actions here if desired */
res.send(task);
});
This is a little more flexible if you want to perform other error-checking; task is declared first so it can be accessible outside the try/catch block, and a 404 error is thrown if the task does not exist.
You can also look at the exists method which will return true or false based on if the document exists, but since you need the actual result that does not make as much sense.
You don't indicate what Task is, but it appears that it is rejecting when it doesn't find anything, rather than returning a false value (which is what you seem to be expecting).
Given that, you should probably just handle the error that it is throwing with something like
} catch ( error ) {
// Will need to adapt this if to something that identifies the error thrown by `getById`
if ( error.message.includes( 'not found' ) ) {
res.status( 404 ).send( 'task not found' );
} else {
res.status( 500 ).send( 'Internal server error' );
}
}
I am having an issue where Intellij is warning me about 'throw' of exception caught locally. After doing some digging on why this is not ok it makes sense, errors should not be used for flow control. The problem I am facing though is in async I cannot reject the promise without throw something locally and I get the warning.
Some of my example code.
Top level takes in the request and awaits for the response from the controller:
Router.post("/", async (req, res) => {
try {
let itemController = new ItemController(req.body);
let response = await itemController.request();
res.send(response);
} catch (error) {
res.status(500).send({ error: error});
}
});
The controller takes in the request and awaits on other functions to get some data.
async request() {
try {
await isValidItem();
return await this.initialize();
} catch(error) {
throw error;
}
}
Then I have a function which gets manufacturer ID for this item and I run into my problem. If the SQL query doesn't fail and nothing is in the response I need to throw a local error so that the request can fail gracefully. and send a proper 500 error to the client.
async queryManufacturerID() {
try {
let result = await this.queryManufacturerID(this.itemID, this.brand);
if (result === false) {
throw new Error("this item has no manufacturer ID");
} else {
this.manufacturerID = result["manufacturerItemID"];
}
} catch (error) {
throw error;
}
}
My problem is I know I can adjust this so other functions that get a reply from this can know that this function failed without a error but that would have to happen in this entire chain to prevent throwing locally. Seems like a lot of bloat.
The only thing that makes this code bloaty and the IDE complain is not throwing errors, but this:
try {
//...
} catch (error) {
throw error;
}
It's a no op. You can safely remove it without changing the logic.
The only case where you should use catch is when you actually plan to handle the error and get the execution back on track.
After doing some digging on why this is not ok it makes sense, errors should not be used for flow control
I disagree. Errors are a part of proper flow control, they allow you to handle unplanned things. Throwing an error if something unexpected occured makes sense, also in this case.