I'm kind of new to express and node.js, and I can't figure out the difference between app.use and app.get. It seems like you can use both of them to send information. For example:
app.use('/',function(req, res,next) {
res.send('Hello');
next();
});
seems to be the same as this:
app.get('/', function (req,res) {
res.send('Hello');
});
app.use() is intended for binding middleware to your application. The path is a "mount" or "prefix" path and limits the middleware to only apply to any paths requested that begin with it. It can even be used to embed another application:
// subapp.js
var express = require('express');
var app = modules.exports = express();
// ...
// server.js
var express = require('express');
var app = express();
app.use('/subapp', require('./subapp'));
// ...
By specifying / as a "mount" path, app.use() will respond to any path that starts with /, which are all of them and regardless of HTTP verb used:
GET /
PUT /foo
POST /foo/bar
etc.
app.get(), on the other hand, is part of Express' application routing and is intended for matching and handling a specific route when requested with the GET HTTP verb:
GET /
And, the equivalent routing for your example of app.use() would actually be:
app.all(/^\/.*/, function (req, res) {
res.send('Hello');
});
(Update: Attempting to better demonstrate the differences.)
The routing methods, including app.get(), are convenience methods that help you align responses to requests more precisely. They also add in support for features like parameters and next('route').
Within each app.get() is a call to app.use(), so you can certainly do all of this with app.use() directly. But, doing so will often require (probably unnecessarily) reimplementing various amounts of boilerplate code.
Examples:
For simple, static routes:
app.get('/', function (req, res) {
// ...
});
vs.
app.use('/', function (req, res, next) {
if (req.method !== 'GET' || req.url !== '/')
return next();
// ...
});
With multiple handlers for the same route:
app.get('/', authorize('ADMIN'), function (req, res) {
// ...
});
vs.
const authorizeAdmin = authorize('ADMIN');
app.use('/', function (req, res, next) {
if (req.method !== 'GET' || req.url !== '/')
return next();
authorizeAdmin(req, res, function (err) {
if (err) return next(err);
// ...
});
});
With parameters:
app.get('/item/:id', function (req, res) {
let id = req.params.id;
// ...
});
vs.
const pathToRegExp = require('path-to-regexp');
function prepareParams(matches, pathKeys, previousParams) {
var params = previousParams || {};
// TODO: support repeating keys...
matches.slice(1).forEach(function (segment, index) {
let { name } = pathKeys[index];
params[name] = segment;
});
return params;
}
const itemIdKeys = [];
const itemIdPattern = pathToRegExp('/item/:id', itemIdKeys);
app.use('/', function (req, res, next) {
if (req.method !== 'GET') return next();
var urlMatch = itemIdPattern.exec(req.url);
if (!urlMatch) return next();
if (itemIdKeys && itemIdKeys.length)
req.params = prepareParams(urlMatch, itemIdKeys, req.params);
let id = req.params.id;
// ...
});
Note: Express' implementation of these features are contained in its Router, Layer, and Route.
Simply
app.use means “Run this on ALL requests”
app.get means “Run this on a GET request, for the given URL”
app.use is the "lower level" method from Connect, the middleware framework that Express depends on.
Here's my guideline:
Use app.get if you want to expose a GET method.
Use app.use if you want to add some middleware (a handler for the HTTP request before it arrives to the routes you've set up in Express), or if you'd like to make your routes modular (for example, expose a set of routes from an npm module that other web applications could use).
app.get is called when the HTTP method is set to GET, whereas app.use is called regardless of the HTTP method, and therefore defines a layer which is on top of all the other RESTful types which the express packages gives you access to.
Difference between app.use & app.get:
app.use → It is generally used for introducing middlewares in your application and can handle all type of HTTP requests.
app.get → It is only for handling GET HTTP requests.
Now, there is a confusion between app.use & app.all. No doubt, there is one thing common in them, that both can handle all kind of HTTP requests.
But there are some differences which recommend us to use app.use for middlewares and app.all for route handling.
app.use() → It takes only one callback.
app.all() → It can take multiple callbacks.
app.use() will only see whether url starts with specified path.
But, app.all() will match the complete path.
For example,
app.use( "/book" , middleware);
// will match /book
// will match /book/author
// will match /book/subject
app.all( "/book" , handler);
// will match /book
// won't match /book/author
// won't match /book/subject
app.all( "/book/*" , handler);
// won't match /book
// will match /book/author
// will match /book/subject
next() call inside the app.use() will call either the next middleware or any route handler, but next() call inside app.all() will invoke the next route handler (app.all(), app.get/post/put... etc.) only. If there is any middleware after, it will be skipped. So, it is advisable to put all the middlewares always above the route handlers.
In addition to the above explanations, what I experience:
app.use('/book', handler);
will match all requests beginning with '/book' as URL. so it also matches '/book/1' or '/book/2'
app.get('/book')
matches only GET request with exact match. It will not handle URLs like '/book/1' or '/book/2'
So, if you want a global handler that handles all of your routes, then app.use('/') is the option. app.get('/') will handle only the root URL.
There are 3 main differences I have found till now. The 3rd one is not so obvious and you may find it interesting. The differences are the same for the express router. That means router.use() and router.get() or other post, put, all, etc methods has also same difference.
1
app.use(path, callback) will respond to any HTTP request.
app.get(path, callback) will only respond to GET HTTP request. In the same way, post, put, etc will respond to their corresponding request. app.all() responds to any HTTP request so app.use() and app.all() are the same in this part.
2
app.use(path, callback) will match the prefix of the request path and responds if any prefix of the request path matches the path parameter. Such as if the path parameter is "/", then it will match "/", "/about", "/users/123" etc.
app.get(path, callback) Here get will match the whole path. Same for other HTTP requests and app.all(). Such as, if the path parameter is "/", then it will only match "/".
3
next('route') doesn't work on the middleware/callback functions of app.use(). It works only on app.get(), app.all() and other similar function of other HTTP requests.
According to express documentation:
next('route') will work only in middleware functions that were loaded by using the app.METHOD() or router.METHOD() functions.
METHOD is the HTTP method of the request that the middleware function
handles (such as GET, PUT, or POST) in lowercase.
From here we will use the keyword METHOD instead of get, post, all, etc.
But what is next('route')?!
Let's see.
next('route')
we see, app.use() or app.METHOD() can take several callback/middleware functions.
From the express documentation:
Middleware functions are functions that have access to the request object (req), the response object (res), and the next middleware function in the application’s request-response cycle. The next middleware function is commonly denoted by a variable named next.
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.
So we see each middleware functions have to either call the next middleware function or end the response.
And this is same for app.use() and app.METHOD().
But sometimes in some conditions, you may want to skip all the next callback functions for the current route but also don't want to end the response right now. Because maybe there are other routes which should be matched. So to skip all the callback functions of the current route without ending the response, you can run next('route'). It will skip all the callback functions of the current route and search to match the next routes.
For Example (From express documentation):
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) {
// send a regular response
res.send('regular')
})
// handler for the /user/:id path, which sends a special response
app.get('/user/:id', function (req, res, next) {
res.send('special')
})
See, here in a certain condition(req.params.id === '0') we want to skip the next callback function but also don't want to end the response because there is another route of the same path parameter which will be matched and that route will send a special response. (Yeah, it is valid to use the same path parameter for the same METHOD several times. In such cases, all the routes will be matched until the response ends). So in such cases, we run the next('route') and all the callback function of the current route is skipped. Here if the condition is not met then we call the next callback function.
This next('route') behavior is only possible in the app.METHOD() functions.
Recalling from express documentation:
next('route') will work only in middleware functions that were loaded by using the app.METHOD() or router.METHOD() functions.
Since skipping all callback functions of the current route is not possible in app.use(), we should be careful here. We should only use the middleware functions in app.use() which need not be skipped in any condition. Because we either have to end the response or traverse all the callback functions from beginning to end, we can not skip them at all.
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app.use gets called every time a request is sent to the server.
Only thing is we should call it before handling get, put, post etc. requests
app.use(middleware);
function middleware(req, res, next)
{
console.log("Came in middleware function without arrow");
next();
}
app.get gets called only for get requests for given path.
app.get('/myget', myget_function);
function myget_function(req, res)
{
console.log("Came in function myget");
res.send('Hello World! from myget');
}
app.post gets called only for post requests for given path.
app.post('/mypost', mypost_function);
function mypost_function(req, res)
{
console.log("Came in function mypost");
res.send('Hello World! from mypost');
}
I am catching all traffic before passing it forward using:
app.all('*', function(req, res, next) {
... run before stuff, related to the next req.route.path
next();
});
and I want to run some code before calling the next() function.
in order for me to know the proper code I need to run, I have to identify what is the next request route path.
Debugging current req object (inside all('*',.. ) does not giving any information about the next request.route.path
How can I get the next method route.path before calling it?
Your help will be appreciated. Thank you.
Instead of trying to look ahead, why not explicitly set middleware for the routes that need it?
var middleware = function (req, res, next) {
..run your code in here
};
app.get('/users:user_id', middleware, function(req, res, next) {
});
You can get the next route by checking the route when the response in the middleware has fired the finish event:
app.all('*', function(req, res, next) {
res.on('finish', function() {
console.log('Next route: ', req.route.path);
});
next();
});
For a route defined like this:
app.get('/users/:user_id', function(req, res) {
res.send('Hello');
});
You'll obtain the log:
$ Next route: '/users/:user_id'
Say I have this code in node.js:
app.post('/stuff', function(req, res){
res.send('hello world');
});
app.route('*').all(function(req,res,next){
res.write('Hello World');
});
There are 2 routes here - one is a catch-all for any request to the server and the other is what to do if a post request with a route of /stuff is sent.
Is it possible to pass a value local to the post request into route?
Intended Program flow: initial request to the server goes through route (which has controls not illustrated to ignore post requests) and the connection is left open, then a post request is sent from the initial request and is dealt with by app.post - can a value found within the closure of post be passed to the initial request that is still open?
I am trying to avoid using Global variables, and res.local only has a local scope. Also trying to keep clean so if I can use native express or node.js all the better. Much obliged for any help.
then a post request is sent from the initial request
Why don't you simply pull out the POST function and call it from both handlers, that way you don't need to send a seperate request from inside your app.
var postHandler = function(req, res) {
res.send('hello world');
// Just return whatever you want back to the calling function
return someValue;
};
// Set it as the handler for post.
app.post('/stuff', postHandler);
app.route('*').all(function(req,res,next){
// Call function.
var returnValue = postHandler(req, res);
res.write('Hello World');
});
app.route('*').all(function(req,res,next){
if (req.originalUrl === '/stuff') {
req.variable = 'some value';
return next();
};
res.write('Hello World');
});
app.post('/stuff', function(req, res){
var value = req.variable;
res.send('hello world');
});
You can try this code. Please take the order of app.all and app.post.
The second way, your can try app.locals http://www.expressjs.com.cn/4x/api.html#app.locals
The app.locals object is a JavaScript object, and its properties are
local variables within the application.
I'm trying to understand JWT and how they work with Node and Express .js. I have this middleware that tries to authenticate users with a token:
app.use(function(req, res, next) {
if(req.headers.cookie) {
var autenticazione = req.headers.cookie.toString().substring(10)
autenticazione = autenticazione.substring(0, autenticazione.length - 3)
console.log(autenticazione)
jwt.verify(autenticazione, app.get('superSegreto'), function(err) {
if (err) {
res.send('authentication failed!')
} else {
// if authentication works!
next() } })
} else {
console.log('errore')} })
And this is the code for my protected url:
app.get('/miao', function (req, res) {
res.sendFile(__dirname + '/pubblica/inserisciutente.html')
res.end() })
Even though the path is correct (I even tried with path.join(__dirname + '/pubblica/inserisciutente.html) and got the same result), when visiting the url I just get a blank page (with even node conde inside) I also set: app.use(express.static('/pubblica')) P.S. if I try to replace res.sendFile(..) with res.send('Some stuff') I can correctly view it on the page. What am I doing wrong?
res.sendFile() is asynchronous and it will end its own response if it is successful.
So, when you call res.end() right after you start res.sendFile() you are ending the response before the code has actually sent the file.
You can do it like this:
app.get('/miao', function (req, res) {
res.sendFile(__dirname + '/pubblica/inserisciutente.html', function(err) {
if (err) {
res.status(err.status).end();
}
});
});
See the Express doc for res.sendFile() here.
if you want to end the response with res.end() then you must not mention or specify it after res.sendFile() because res.sendFile() is an asynchronous function that means it will take some time to execute and in that meantime next instruction which is in your case is res.end() will execute and that's why you didn't see any response send by the res.sendFile
You can visit the documentation to know more about res.sendFile() visit documentation
I'm new to Node and Express and I'm not sure how I can access req in a middleware function in a POST route. Do I need to pass it in as a parameter? There are other middleware functions in this route that access req but it is not being passed in. Overall, I'm guess I'm confused as to how req works...
The function I'm referring to is helpers.createPermissions()
My Route
app.post('/oauth/authorize/decision', login.ensureLoggedIn('connect/signin'), helpers.createPermissions(req), oauth2.server.decision());
The Function
exports.createPermissions = function(req) {
console.log(req);
};
The Error
ReferenceError: req is not defined
Middleware will always get passed three arguments: req, res and next.
So your middleware should look like this:
exports.createPermissions = function(req, res, next) {
console.log(req);
// TODO: make sure you eventually call either `next` or send back a response...
};
And you can use it like this:
app.post('/oauth/authorize/decision', login.ensureLoggedIn('connect/signin'), helpers.createPermissions, oauth2.server.decision());
In situations where you see middleware being called as a function, it's because you're not calling the middleware itself, but a function that's returning a middleware function. For example:
var myMiddlewareWrapper = function() {
// return the actual middleware handler:
return function(req, res, next) {
...
};
};
app.get('/', myMiddlewareWrapper(), ...);
This is usually done to pass extra options to the middleware handler (like with login.ensureLoggedIn()).