When to skip error handling? I don't think this make sense
exports function getItems(req, res, next) => {
Item.find({}, function(err, items){
if(err) throw Error()
res.json(items)
})
}
Because get will not fail most of the time. I'm sick of writing error handling in node. Now I skip GET request, just do handling for POST, PUT or DELETE.
I'm using async await, I have to do try catch in every GET, that's annoying.
router.get('/user/:id', async (req, res, next) => {
try {
const user = await getUserFromDb({ id: req.params.id })
res.json(user);
} catch (e) {
next(e)
}
})
Related
I have the following endpoint:
app.get('/users/:id', async (req, res) => {
const _id = req.params.id;
try {
const user = await User.findById(_id);
if(!user) {
res.status(404).send();
}
res.send(user);
} catch (e) {
res.status(500).send(e);
}});
When I make the request with a valid user ID, the server sends back the user, no problem with that.
The problem is when I try to find a user with a ID which doesnt exist in the database. The server should response with a 404 Error but instead it sends back a Error 500 and I dont understand why!
Could anyone help me please?
Thank you in advance!
One nice way to handle the errors is to create an express error middleware, this allows you to put all of your error handling in one place so that you dont have to write it more than once.
With express when you use async routes handlers if a promise rejects the error will automatically be passed to the next error middleware.
// First register all of your routes
app.get('/user/:id', async (req, res) => {
const user = await User.findById(req.params.id);
if(!user) return res.status(404).send();
res.send(user);
})
// Then register you error middleware
app.use((err, req, res, next) => {
console.error(err.message)
// if mongoose validation error respond with 400
if(err.message.toLowerCase().includes('validation failed'))
return res.sendStatus(400)
// if moongoose failed because of duplicate key
if(err.message.toLowerCase().includes('duplicate key'))
return res.sendStatus(409)
// if mongoose failed to cast object id
if(err.message.toLowerCase().includes('objectid failed'))
return res.sendStatus(404)
res.sendStatus(500)
})
Thank you for your answers.
I have solved it adding the following to the user model schema:
_id: {type: String}
And adding a return before sending the 404 error:
app.get('/users/:id', async (req, res) => {
const _id = req.params.id;
try {
const user = await User.findById(_id);
if (!user) {
return res.status(404).send();
}
res.send(user);
} catch (error) {
res.status(400).send(error);
}});
I have a problem right now that I can't solve by myself. I assume you know more here. I'm just getting started.
By using the following code I'm getting a list of customers:
app.get("/customers", customers.findAll);
I wanted to add authentication. But now I don't know how to execute "customers.findAll" and get the value as JSON.
app.get("/customers", verifyToken, (req, res) => {
jwt.verify(req.token, 'justAtest, (err, authData) => {
if (err) {
res.sendStatus(403);
} else {
// execute customers.findAll
}
});
});
Customers is integrated via a requirement
const customers = require("../controllers/customer.controller.js");
The contents are as follows:
exports.findAll = (req, res) => {
Customer.getAll((err, data) => {
if (err)
res.status(500).send({
message:
err.message || "Some error occurred while retrieving customers."
});
else res.send(data);
});
};
Do you have any ideas?
Thank you in advance.
Grettings
Rok
You achieve that using something called "middleware". Explore it since it is very important.
Basically :
app.get("/customers", verifyToken,customers.findAll);
Wherre verify token is a funtion that has 3 parameters: req, res and 3rd one called "next".
So your verify token function would look something like:
(req, res,next) => {
jwt.verify(req.token, 'justAtest, (err, authData) => {
if (err) {
res.sendStatus(403);
} else {
next();
}
});
}
I took it from your snippet. Basically if you want to jump to customeeers.finalAll, just call "next" and it jumps to next function :D.
I have an async middleware in express, because I want to use await inside it, to clean up my code.
const express = require('express');
const app = express();
app.use(async(req, res, next) => {
await authenticate(req);
next();
});
app.get('/route', async(req, res) => {
const result = await request('http://example.com');
res.end(result);
});
app.use((err, req, res, next) => {
console.error(err);
res
.status(500)
.end('error');
})
app.listen(8080);
The problem is that when it rejects, it doesn't go to my error middleware, but if I remove the async keyword and throw inside a middleware it does.
app.get('/route', (req, res, next) => {
throw new Error('Error');
res.end(result);
});
So I'm getting UnhandledPromiseRejectionWarning instead of entering my error handling middleware, how can I let the error bubble up, and express handle it?
The problem is that when it rejects, it doesn't go to my error
middleware, but if I remove the async keyword and throw inside a
middleware it does.
express doesn't support promises currently, support may come in the future release of express#5.x.x
So when you pass a middleware function, express will call it inside a try/catch block.
Layer.prototype.handle_request = function handle(req, res, next) {
var fn = this.handle;
if (fn.length > 3) {
// not a standard request handler
return next();
}
try {
fn(req, res, next);
} catch (err) {
next(err);
}
};
The problem is that try/catch won't catch a Promise rejection outside of an async function and since express does not add a .catch handler to the Promise returned by your middleware, you get an UnhandledPromiseRejectionWarning.
The easy way, is to add try/catch inside your middleware, and call next(err).
app.get('/route', async(req, res, next) => {
try {
const result = await request('http://example.com');
res.end(result);
} catch(err) {
next(err);
}
});
But if you have a lot of async middlewares, it may be a little repetitive.
Since I like my middlewares as clean as possible, and I usually let the errors bubble up, I use a wrapper around async middlewares, that will call next(err) if the promise is rejected, reaching the express error handler and avoiding UnhandledPromiseRejectionWarning
const asyncHandler = fn => (req, res, next) => {
return Promise
.resolve(fn(req, res, next))
.catch(next);
};
module.exports = asyncHandler;
Now you can call it like this:
app.use(asyncHandler(async(req, res, next) => {
await authenticate(req);
next();
}));
app.get('/async', asyncHandler(async(req, res) => {
const result = await request('http://example.com');
res.end(result);
}));
// Any rejection will go to the error handler
There are also some packages that can be used
async-middleware
express-async-handler
Well, I found this - https://github.com/davidbanham/express-async-errors/, then require the script and you are good to go
const express = require('express');
require('express-async-errors');
Answer with asyncHandler is good and usefull, but it is still not comfortable to write this wrapper in every route. I propose to improve it:
const asyncHandler = fn => (req, res, next) => {
return Promise
.resolve(fn(req, res, next))
.catch(next)
}
const methods = [
'get',
'post',
'delete' // & etc.
]
function toAsyncRouter(router) {
for (let key in router) {
if (methods.includes(key)) {
let method = router[key]
router[key] = (path, ...callbacks) => method.call(router, path, ...callbacks.map(cb => asyncHandler(cb)))
}
}
return router
}
and now we can do that way:
const router = toAsyncRouter(express().Router())
router.get('/', someAsyncController)
and so one.
Minute ago added a npm module async-express-decorator.
You need to use try-catch and in catch section just pass the error in next() parameter Like this -
async create(req, res, next) {
try {
const userProp = req.body;
const user = new User(userProp)
const response = await user.save()
const token = await user.createJWSToken()
res.send({response, token})
} catch (err){
next(err)
}
}
And obviously put this express middleware on your index.js file.
app.use((err, req, res, next) => {
res.status(422).send({ error: err.message });
});
Express 5 now handle async promises:
https://expressjs.com/en/guide/error-handling.html
Starting with Express 5, route handlers and middleware that return a
Promise will call next(value) automatically when they reject or throw
an error. For example
You need to callbackify your async handler. If you know the concept of promisify, this is the opposite. Callbackify is built-in in Node.
import util from 'util'
app.use(util.callbackify(async (req, res) => {
await authenticate(req);
}));
What this does is that it returns a function with a third argument which would be the next function and calls it after the promise has been resolved. If the promise is rejected, the next function will be called with the error as an argument.
Suppose I have a route like this:
app.get('/broken', (req, res) => {
throw new Error('Broken!');
});
This will never send a response to clients.
However, I can add a middleware for all errors:
const errorMiddleware = (error, req, res, next) => {
if (error) {
console.error(error);
return res.status(500)
.json({
message: 'Internal server error',
});
}
next(error);
};
But this will not work for async routes, because they do not throw directly.
For example, this will not work:
app.get('/broken', async (req, res) => {
throw new Error('Broken!');
});
So I can create a wrapper like this:
const asyncRoute = f => (req, res, next) => {
return Promise.resolve(f(req, res, next)).catch(next);
};
app.get('/broken', asyncRoute(async (req, res) => {
throw new Error('Broken!');
}));
But this is a real pain, because now I have to call this function for every route!
What is a better way of handling this?
The answer to Is there a way to wrap an await/async try/catch block to every function? is just what I describe above
The answer to how to use Promise with express in node.js? does not use await
Fundamentally, you don't want to directly pass an async function into Express's app.get, because app.get doesn't handle the promise the function returns. So you'll need to wrap those async handlers (as you're doing).
You can avoid having to do it every time by giving yourself a utility method at the top of the module:
const appGet = handler => app.get(asyncRoute(handler));
then use it instead of app.get:
appGet('/broken', async (req, res) => {
throw new Error('Broken!');
});
At some point (probably not right now), you might want to look at Koa.
I have the following code :
server.use(function(req, res, next) {
users_db.set(req.user, function(err) { // async call to mongodb
if (err) {
console.error(err);
}
});
}
return next();
});
server.get('/', function(req, res) {
req.user.active = true; // this is a new field in user object
res.send(req.user);
}
});
So, As you see, when users_db.set() is called, req.user doesn't have the active=true field. It is being inserted only in the server.get() function.
Is it possible that user.active = true is registered in the db nevertheless because of the asynchronous nature of the call ?
As far as I know (it is like that in Express at least) .get method accepts many middleware functions. So I guess that the following will work:
server.get(
'/',
function(req, res, next) {
req.user.active = true; // this is a new field in user object
res.send(req.user);
next();
},
function(req, res, next) {
users_db.set(req.user, function(err) { // async call to mongodb
if (err) {
console.error(err);
}
});
}
return next();
}
);
Doing the things like that you are sure that req.user.active is populated always before to reach the moment with users_db.set.