I have this helper :
function loginRequired(msg){ // this is the helper
return function(req, res, next){
if (req.user.is_authenticated){ // example
return next()
}
//else
req.flash('error_msg',msg)
return res.redirect('/')
}
}
and I have this route ( I`m using the helper in this route ) :
router.post('/new', loginRequired(msg='You are not allowed here'), async (req, res)=>{
// code
})
The problem is that the function returned by the helper is not being executed, when I request this route, it keeps loading forever and the content is never sent.
There isn't anything obviously wrong with the loginRequired() function and how you're using it so the problem is probably elsewhere. The only thing I see is that if req.user doesn't exist, then it would throw.
For further debugging, I would suggest you do this to make sure your route is being matched.
function logRoute(msg) {
return function(req, res, next) {
console.log(msg);
next();
}
}
router.post('/new', logRoute("/new handler"), loginRequired(msg='You are not allowed here'), async (req, res)=>{
// code
});
And, make sure you see /new handler in the console. If you don't even see that, then the problem is further upstream with how your route is declared as it isn't matching an incoming request. You would have to show us the rest of that code for us to see how the router is being used.
I am a tyro in node and express, learning the things. I was reading Express's documentation at this link: https://expressjs.com/en/guide/routing.html and in the Route Handlers section of this page, it says:
You can provide multiple callback functions that behave like middleware to handle a request. The only exception is that these callbacks might invoke next('route') to bypass the remaining route callbacks.
The examples given on this page doesn't contain any next() with arguments in it.
I tried implementing it and passing some path as an argument in this function but it behaves strangely and prints that argument in the console and also sends it to the browser.
Below is my code:
const express = require('express');
const port = 8000;
const app = express();
app.get('/', (req, res, next) => {
console.log("I am the first one");
next('/demo');
}, function(req, res, next){
console.log("I am the second one");
});
app.get('/demo', (req, res) => {
console.log("Good!");
});
app.listen(port, (err) => {
if(err){
console.log("ERROS: ",err);
}
console.log("Express server is runnig on port: ",port);
});
In the browser, I typed http://localhost:8000/The output in console is:
I am the first one
/demo
the next('/demo') function call doesn't cause /demo route handler to run.
Where am I going wrong?
Am I getting it right?
Actually I am not able to understand how this argument thing works with the next() function.
Since the documentation page does not have any example with arguments in function, Can anyone please explain how this next() function work with arguments through an example?
Thanks in advance for any help you are able to provide
I did some deep diving here because it seemed interesting to me and then I realized it's just the error being returned. Let me explain.
Basically next() which is a expressjs specific functionality is used to pass over the control to next functional unit. It doesn't expect parameters of string, barring one (given below - after the error piece). That even in a case when you initialize it properly.
Here is the output in the network tab once you load the page, please check.
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Error</title>
</head>
<body>
<pre>/demo</pre>
</body>
</html>
NOTE: next('route') will work only in middleware functions that were
loaded by using the app.METHOD() or router.METHOD() functions.
You cannot call another router the way you are doing at the moment, http will have one response for one request to close the channel. However you can do something like.
app.get('/', (req, res, next) => {
console.log("I am the first one");
next();
}, function(req, res, next){
console.log("I am the second one");
next();
});
app.get('/', (req, res, next) => {
console.log("I am the third one");
next();
}, function(req, res, next){
console.log("I am the fourth one");
});
Here middleware works it's magic and matches whatever identical route parameter is and goes on to execute it all.
The next() function in
app.get('/', (req,...
used to call the next callback in the same route
...
function(req, res, next){
console.log("I am the second one");
});
Once you remove the /demo from the next('/demo'), you will notice "I am the second one" in the console. NOTE: next() only passes the control to the next middleware in the same route.
app.get('/', (req, res, next)=>{
// E.g. purpose of this middleware is to print request method
console.log('Request method:', req.method)
next() // this code passes the control to the next callback which is below
}, (req, res) => {
console.log('End of route')
res.send('OK')
}
It does not engage the app's route. In order to go to another route, you have to send another HTTP request. Hope this helps!
UPDATE Here's the scenario where next('route') does something, this only works if 2 routes are of the same URI and http method.
const express = require('express')
const app = express();
function middleware1(req, res, next){
console.log('Middleware #1')
next('route') // ends current callback chain, moves to the next route
}
app.get('/', middleware1, (req, res, next)=>{
console.log('Second middleware') // this callback is not executed
res.send('OK')
})
app.get('/', (req, res)=>{
console.log('Test') // the callback in this route gets called
res.send('2nd get / OK')
})
app.listen(3000, () => {
console.log('Server #', 3000)
})
I think this implementation of route is seldom being put into practice because personally I feel that it is tedious to follow (having 2 routes with the same uri and http method). Nonetheless it is good to learn something from Gandalf the White and this.
There are a few posts on this question but none that answers the issue directly, head-on. Let me clarify that I understand (or so I think) the use of next(), next('route'), return next(), return and their impact on control flow.
My entire middleware for the app consists of a series of app.use, as in:
app.use(f1);
app.use(f2);
app.use(f3);
app.use(f4);
...
In each of these middlewares, I have possibility of sending the response and be done without any need for further processing. My problem is that I am unable to stop the processing from going to the next middleware.
I have a clumsy work around. I just set a res.locals.completed flag after sending a response. In all the middlewares, at the very start, I check this flag and skip processing in the middleware if the flag is set. In the very first middleware, this flag is unset.
Surely, there must be a better solution, what is it? I would think that Express implicitly would do this checking and skip the middlewares through some express-specific method?
According to the express documentation on http://expressjs.com/guide/using-middleware.html
If the current middleware does not end the request-response cycle,
it must call next() to pass control to the next middleware,
otherwise the request will be left hanging.
so if a middleware needs to end the request-response early, simply do not call next() but make sure that the middleware really ends the request-response by calling res.end, res.send, res.render or any method that implicitely calls res.end
app.use(function (req, res, next) {
if (/* stop here */) {
res.end();
} else {
next();
}
});
Here is an example server showing that it works
var express = require('express');
var app = express();
var count = 0;
app.use(function(req, res, next) {
console.log('f1');
next();
})
app.use(function(req, res, next) {
console.log('f2');
if (count > 1) {
res.send('Bye');
} else {
next();
}
})
app.use(function(req, res, next) {
console.log('f3');
count++;
next();
})
app.get('/', function (req, res) {
res.send('Hello World: ' + count);
});
var server = app.listen(3000);
you will see the after 3 requests, the server shows "Bye" and f3 is not reached
I'm trying to log every request made to my sails application, but I can't find a way to log the response associated with a request.
I added this custom middleware in the config/http.js file :
myRequestLogger: function (req, res, next) {
req.on("end", function(){
sails.log(res.statusCode);
});
return next();
}
But it doesn't work properly, I can get the 200 codes, buta res.forbidden or res.notFound response is not logged. Any idea about how I could handle that ?
Thank you
You can override that in api/responses itself. Here is simplified override:
// api/responses/forbidden.js
module.exports = function(err, viewOrRedirect) {
// ... Sails logic
this.req._sails.log.verbose();
}
But, if you expect that your middleware above can do this, you're wrong. Your middleware should looks similar to this:
myRequestLogger: function(req, res, next) {
req._sails.log.verbose('YOUR LOG');
return next();
}
Ok, I have found the answer by reading this stackoverflow post : https://stackoverflow.com/a/11841877/2700309
Apparently there is a 'finish' event emitted just before the response is send to the client. So the right code would be :
myRequestLogger: function (req, res, next) {
res.on("finish", function(){
sails.log(res.statusCode);
});
return next();
}
And this seems to work!
Have been trying to find a good description of what the next() method does. In the Express documentation it says that next('route') can be used to jump to that route and skip all routes in between, but sometimes next is called without arguments. Anybody knows of a good tutorial etc that describes the next function?
next() with no arguments says "just kidding, I don't actual want to handle this". It goes back in and tries to find the next route that would match.
This is useful, say if you want to have some kind of page manager with url slugs, as well as lots of other things, but here's an example.
app.get('/:pageslug', function(req, res, next){
var page = db.findPage(req.params.pageslug);
if (page) {
res.send(page.body);
} else {
next();
}
});
app.get('/other_routes', function() {
//...
});
That made up code should check a database for a page with a certain id slug. If it finds one render it! if it doesn't find one then ignore this route handler and check for other ones.
So next() with no arguments allows to pretend you didn't handle the route so that something else can pick it up instead.
Or a hit counter with app.all('*'). Which allows you to execute some shared setup code and then move on to other routes to do something more specific.
app.all('*', function(req, res, next){
myHitCounter.count += 1;
next();
});
app.get('/other_routes', function() {
//...
});
In most frameworks you get a request and you want to return a response. Because of the async nature of Node.js you run into problems with nested call backs if you are doing non trivial stuff. To keep this from happening Connect.js (prior to v4.0, Express.js was a layer on top of connect.js) has something that is called middleware which is a function with 2, 3 or 4 parameters.
function (<err>, req, res, next) {}
Your Express.js app is a stack of these functions.
The router is special, it's middleware that lets you execute one or more middleware for a certain url. So it's a stack inside a stack.
So what does next do? Simple, it tells your app to run the next middleware. But what happens when you pass something to next? Express will abort the current stack and will run all the middleware that has 4 parameters.
function (err, req, res, next) {}
This middleware is used to process any errors. I like to do the following:
next({ type: 'database', error: 'datacenter blew up' });
With this error I would probably tell the user something went wrong and log the real error.
function (err, req, res, next) {
if (err.type === 'database') {
res.send('Something went wrong user');
console.log(err.error);
}
};
If you picture your Express.js application as a stack you probably will be able to fix a lot of weirdness yourself. For example when you add your Cookie middleware after you router it makes sense that your routes wont have cookies.
Docs
How do I setup an error handler?
Error Handling
You define error-handling middleware in the same way as other middleware, except with four arguments instead of three; specifically with the signature (err, req, res, next):
app.use(function (err, req, res, next) {
console.error(err.stack)
res.status(500).send('Something broke!')
})
IMHO, the accepted answer to this question is not really accurate. As others have stated, it's really about controlling when next handler in the chain is run. But I wanted to provide a little more code to make it more concrete. Say you have this simple express app:
var express = require('express');
var app = express();
app.get('/user/:id', function (req, res, next) {
console.log('before request handler');
next();
});
app.get('/user/:id', function (req, res, next) {
console.log('handling request');
res.sendStatus(200);
next();
});
app.get('/user/:id', function (req, res, next) {
console.log('after request handler');
next();
});
app.listen(3000, function () {
console.log('Example app listening on port 3000!')
});
If you do
curl http://localhost:3000/user/123
you will see this printed to console:
before request handler
handling request
after request handler
Now if you comment out the call to next() in the middle handler like this:
app.get('/user/:id', function (req, res, next) {
console.log('handling request');
res.sendStatus(200);
//next();
});
You will see this on the console:
before request handler
handling request
Notice that the last handler (the one that prints after request handler) does not run. That's because you are no longer telling express to run the next handler.
So it doesn't really matter if your "main" handler (the one that returns 200) was successful or not, if you want the rest of the middlewares to run, you have to call next().
When would this come in handy? Let's say you want to log all requests that came in to some database regardless of whether or not the request succeeded.
app.get('/user/:id', function (req, res, next) {
try {
// ...
}
catch (ex) {
// ...
}
finally {
// go to the next handler regardless of what happened in this one
next();
}
});
app.get('/user/:id', function (req, res, next) {
logToDatabase(req);
next();
});
If you want the second handler to run, you have to call next() in the first handler.
Remember that node is async so it can't know when the first handler's callback has finished. You have to tell it by calling next().
next() without parameter invokes the next route handler OR next middleware in framework.
Summarizing rightly mentioned answers in one place,
next() : move control to next function in same route. case of
multiple functions in single route.
next('route') :move control to next route by skipping all remaining
function in current route.
next(err) : move control to error middleware
app.get('/testroute/:id', function (req, res, next) {
if (req.params.id === '0') next() // Take me to the next function in current route
else if (req.params.id === '1') next('route') //Take me to next routes/middleware by skipping all other functions in current router
else next(new Error('Take me directly to error handler middleware by skipping all other routers/middlewares'))
}, function (req, res, next) {
// render a regular page
console.log('Next function in current route')
res.status(200).send('Next function in current route');
})
// handler for the /testroute/:id path, which renders a special page
app.get('/testroute/:id', function (req, res, next) {
console.log('Next routes/middleware by skipping all other functions in current router')
res.status(200).send('Next routes/middleware by skipping all other functions in current router');
})
//error middleware
app.use(function (err, req, res, next) {
console.log('take me to next routes/middleware by skipping all other functions in current router')
res.status(err.status || 500).send(err.message);
});
Question also asked about use of next('route') which seems to be covered week in provided answers so far:
USAGE OF next():
In short: next middleware function.
Extract from this official Express JS documentation - 'writing-middleware' page:
"The middleware function myLogger simply prints a message, then passes on the request to the next middleware function in the stack by calling the next() function."
var express = require('express')
var app = express()
var myLogger = function (req, res, next) {
console.log('LOGGED')
next()
}
app.use(myLogger)
app.get('/', function (req, res) {
res.send('Hello World!')
})
app.listen(3000)
This page of Express JS documentation states "If the current middleware function does not end the request-response cycle, it must call next() to pass control to the next middleware function. Otherwise, the request will be left hanging."
USAGE OF next('route') :
In short: next route (vs. next middleware function in case of next() )
Extract from this Express JS documentation - 'using-middleware' page:
"To skip the rest of the middleware functions from a router middleware stack, call next('route') to pass control to the next route. NOTE: next('route') will work only in middleware functions that were loaded by using the app.METHOD() or router.METHOD() functions.
This example shows a middleware sub-stack that handles GET requests to the /user/:id path."
app.get('/user/:id', function (req, res, next) {
// if the user ID is 0, skip to the next route
if (req.params.id === '0') next('route')
// otherwise pass the control to the next middleware function in this stack
else next()
}, function (req, res, next) {
// render a regular page
res.render('regular')
})
// handler for the /user/:id path, which renders a special page
app.get('/user/:id', function (req, res, next) {
res.render('special')
})
Its simply means pass control to the next handler.
Cheers
Notice the call above to next(). Calling this function invokes the next middleware function in the app. The next() function is not a part of the Node.js or Express API, but is the third argument that is passed to the middleware function. The next() function could be named anything, but by convention, it is always named “next”. To avoid confusion, always use this convention.
next() is the callback argument to the middleware function with req, and res being the http request and response arguments to next in the below code.
app.get('/', (req, res, next) => { next() });
So next() calls the passed in middleware function. If current middleware function does not end the request-response cycle, it should call next(), else the request will be left hanging and will timeout.
next() fn needs to be called within each middleware function when multiple middleware functions are passed to app.use or app.METHOD, else the next middleware function won’t be called (incase more than 1 middleware functions are passed). To skip calling the remaining middleware functions, call next(‘route’) within the middleware function after which no other middleware functions should be called. In the below code, fn1 will be called and fn2 will also be called, since next() is called within fn1. However, fn3 won’t be called, since next(‘route’) is called within fn2.
app.get('/fetch', function fn1(req, res, next) {
console.log("First middleware function called");
next();
},
function fn2(req, res, next) {
console.log("Second middleware function called");
next("route");
},
function fn3(req, res, next) {
console.log("Third middleware function will not be called");
next();
})