Related
I'm starting with NodeJS and Express 4, and I'm a bit confused. I been reading the Express website, but can't see when to use a route handler or when to use express.Router.
As I could see, if I want to show a page or something when the user hits /show for example I should use:
var express = require('express')
var app = express()
app.get("/show", someFunction)
At the beginning, I thought this was old (for Express 3). Is that right or this is the way for Express 4 too?
If this is the way to do it in Express 4, what is express.Router used for?
I read almost the same example as above but using express.Router:
var express = require('express');
var router = express.Router();
router.get("/show", someFunction)
So, what's the difference between both examples?
Which one should I use if I just want to do a simple testing website?
app.js
var express = require('express'),
dogs = require('./routes/dogs'),
cats = require('./routes/cats'),
birds = require('./routes/birds');
var app = express();
app.use('/dogs', dogs);
app.use('/cats', cats);
app.use('/birds', birds);
app.listen(3000);
dogs.js
var express = require('express');
var router = express.Router();
router.get('/', function(req, res) {
res.send('GET handler for /dogs route.');
});
router.post('/', function(req, res) {
res.send('POST handler for /dogs route.');
});
module.exports = router;
When var app = express() is called, an app object is returned. Think of this as the main app.
When var router = express.Router() is called, a slightly different mini app is returned. The idea behind the mini app is that each route in your app can become quite complicated, and you'd benefit from moving all that code into a separate file. Each file's router becomes a mini app, which has a very similar structure to the main app.
In the example above, the code for the /dogs route has been moved into its own file so it doesn't clutter up the main app. The code for /cats and /birds would be structured similarly in their own files. By separating this code into three mini apps, you can work on the logic for each one in isolation, and not worry about how it will affect the other two.
If you have code (middleware) that pertains to all three routes, you can put it in the main app, before the app.use(...) calls. If you have code (middleware) that pertains to just one of those routes, you can put it in the file for that route only.
Express 4.0 comes with the new Router. As mentioned on the site:
The express.Router class can be used to create modular mountable route
handlers. A Router instance is a complete middleware and routing
system; for this reason it is often referred to as a “mini-app”.
There is a good article at https://scotch.io/tutorials/learn-to-use-the-new-router-in-expressjs-4 which describes the differences and what can be done with routers.
To summarize
With routers you can modularize your code more easily. You can use routers as:
Basic Routes: Home, About
Route Middleware to log requests to the console
Route with Parameters
Route Middleware for Parameters to validate specific parameters
Validates a parameter passed to a certain route
Note:
The app.router object, which was removed in Express 4, has made a comeback in Express 5. In the new version, it is a just a reference to the base Express router, unlike in Express 3, where an app had to explicitly load it.
How they are different
Everyone, including the documentation, tends to refer back to how much they are the same, but not actually reference any differences. Well, they are, in fact, different.
var bigApp = express();
var miniApp = express.Router();
listen()
The most obviously difference is that the bigApp will give listen, which just a rather confusing way to do what would otherwise be simple and obvious the node http or https module:
var server = require('http').createServer(bigApp);
server.listen(8080, function () {
console.info(server.address());
});
I consider this an anti-pattern because it abstracts and obscures away something that wasn't complicated or difficult in the first place, and then makes it difficult for people to use websockets and other middleware that require the raw http server.
Internal State
The big difference, which is really important, is that all bigApps have separate internal state.
bigApp.enable('trust proxy');
bigApp.enabled('trust proxy');
// true
var bigApp2 = express();
bigApp2.enabled('trust proxy');
// false
bigApp.use('/bunnies', bigApp2);
// WRONG! '/bunnies' will NOT trust proxies
A miniApp passed to a bigApp, however, will be operated by the bigApp in such a way that its internal state and thisness will be preserved and those routes will behave accordingly.
bigApp.enable('trust proxy');
bigApp.enabled('trust proxy');
// true
var miniApp = express.Router();
bigApp.use('/bunnies', miniApp);
// CORRECT! All state and such are preserved
This can be a big deal because express does a lot of (sometimes trixy) things to the http.ServerRequest and httpServerResponse object - such as modifying (or hijacking) req.url and req.originalUrl and various other properties you've been using without realizing - and you probably don't want that duplicated and separated.
Smaller API
There is a smaller, more well-defined number of functions a Router can use:
.use(mount, fn)
.all(mount, fn)
.options(mount, fn)
.head(mount, fn)
.get(mount, fn)
.post(mount, fn)
.patch(mount, fn)
.put(mount, fn)
.delete(mount, fn)
.route(mount).XXXX
.param(name, cb).XXXX
There are a few other convenience methods as well, such as basic(), but you won't find set() or enable() or other methods that change the larger app state.
app.route('/book')
.get(function (req, res) {
res.send('Get a random book')
})
.post(function (req, res) {
res.send('Post a random book')
})
As in above example, we can add different HTTP request method under a route.
Let’s say your application is little complex. So what we do first is we divide the application into multiple modules so that changes in one module doesn't clutter the others and you can keep working on individual modules, but at the end of the day you need to integrate everything into one since you are building a single application. It is like we have one main application and few child applications whose parent is the main application.
So when we create the parent application we create one using
const express = require("express");
const parent = express();
And to this parent application we need to bring in the child applications. But since the child applications are not totally different applications (since they run in the same context - java term), express provides the way to do it by means on the Express's Router function and this is what we do in the each child module file and lets call one such child module as aboutme.
const express = require("express");
export const router = express.Router();
By export we are making this module available for other to consume and since we have modularized things we need to make the module files available to the parent application by means of node's require function just like any other third party modules and the parent file looks something like this:
const express = require("express");
const parent = express();
const child = require("./aboutme");
After we make this child module available to the parent, we need to tell the parent application when to use this child application. Lets say when a user hits the path aboutme we need the child application about me to handle the request and we do it by using the Express's use method:
parent.use("/aboutme", child);
and in one shot the parent file looks like this:
const express = require("express");
const parent = express();
const child = require("./aboutme");
parent.use("/aboutme", child);
Above all what the parent can do is it can start a server where as the child cannot. Hope this clarifies. For more information you can always look at the source code which takes some time but it gives you a lot of information.
using app.js to write routes means that they are accessible to all the users as app.js is loaded on application start. However, putting routes in express.router() mini apps protect and restrict their accessibility.
In a word , express.Routercan do more things when compares to app.get(),such as middleware, moreover, you can define one more router object with express.Router()
express.Router has many options:
enable case sensitivity: /show route to not be the same as /Show, this behavior is disabled by default
strict routing mode: /show/ route to not the same as /show, this behavior is also disabled by default
we can add specific middleware/s to specific routes
In one of the questions in the quiz this was asked: "express.Router() creates an object that behaves similar to the app object."
The correct answer is 'True'. I know that we can both create routers by using either of the two but is it safe to say that they are not the same in all cases? If my understanding is correct, the express() variable can do more things like start a server while the other one cannot.
In a complicated application, app is module, for example article and user. router is controller or action in module, for example article create and list.
E.g the url https://example.com/article/create parse article module and create router.
also app and router can be level-in-level.
I am overall clueless about how and why you set up a node.js app, and how any of the app.use functions work - the tutorials on it don't explain the why of anything.
Anyway, I have socket.io, res.locals and index.js set up like so in the app.js root file.
const sockets = require('./models/socket')(io)
app.use(function (req, res, next) {
res.locals.user_id = req.session.user_id;
next();
});
const routes = require('./routes/index');
app.use('/', routes);
I'd like to be able to access res.locals in the socket.js model, like I can in index.js found in the routes folder.
I can't guess how to go about doing this. If anybody is able to explain how and why I can or can't that would be a bonus. Thanks!
Welcome to Expressjs, there are a few fundamentals you should probably research before going any further, they'll help solve some of your confusion. I'll give a brief explanation of them but I suggest you do further research. I'll then answer your actual question at the end.
Middleware and app.use
Expressjs is built upon an idea that everything is just "middleware". Middleware is a function which runs as part of a request chain. A request chain is essentially a single client request, which then goes through a chain of a number of middleware functions until it either reaches the end of the chain, exits early by returning a response to the client, or errors.
Express middleware is a function which takes the following three arguments.
req (request) - Representing the request made by a client to your
server.
res (response) - Representing the response you will return to
the client.
next - A way of telling express that your current
middleware function is done, and it should now call the next piece of
middleware. This can either be called "empty" as next(); or with an
error next(new Error());. If it is called empty, it will trigger
the next piece of middleware, if it is called with an error then it
will call the first piece of error middleware. If next is not called at the
end of a piece of middleware, then the request is deemed finished and the
response object is sent to the user.
app.use is a way of setting middleware, this means it will run for every request (unless next() is either not called by the previous piece of middleware for some reason, or it's called with an error). This middleware will run for any HTTP request type (GET, POST, PUT, DELETE, etc).
app.use can take multiple arguments, the important ones for beginners to learn are: app.use(func) and app.use(path, func). The former sets "global" middleware which runs no matter what endpoint (url path) the client requests, the latter (with a specific path) is run only if that specific path is hit. I.e. app.use('/hello', (req, res, next) => { res.send('world'); }); will return "world" when the endpoint "/hello" is hit, but not if the client requests "/hi". Where as app.use((req, res, next) => { res.send('world'); }); would return "world" when you hit any endpoint.
There are more complex things you can do with this, but that's the basics of attaching middleware to your application. The order they are attached to the application, is the order in which they will run.
One more thing, this will blow your mind, an express application made with the standard const app = express() can also be used as middleware. This means you can create several express applications, and then mount them using app.use to a single express application. This is pretty advanced, but does allow you to do some really great things with Express.
Why can you not access res.locals in socket.io? (The real question)
Within your middleware handler, you are setting up a res.locals.use_id property. This only lives with that individual request, you can pass it around as long as the request is alive by passing it into other functions, but outside of that request it doesn't exist. res is literally the response object that tells Express how to respond to the clients request, you can set properties of it during the request but once that HTTP request has ended it's gone.
Socket.io is a way of handling web socket requests, not standard HTTP requests. Thus, in a standard express HTTP request you will not be able to hand off the connection to anything with socket.io, because the connection is a single short lived HTTP request. Likewise, you won't be able to do the same the other way.
If you wish to find the users id in a socket.io request, you'll have to do this within the socket.io request itself.
Right now, you're entering a piece of middleware for an Express.js request, you are then calling next() which runs the next piece of express middleware, at no point does it cross over into Socket.io realms. This is often confused by tutorials because Socket.io can handle requests across the same port as Express is listening on, but the two are not crossed over. So you will need to write separate middleware for both Express.js requests chains, and socket.io request chains. There are ways of writing this code once and then writing an adapter to use it across both platforms, but that's not what you've tried to do here.
I would suggest you look at doing just nodejs and express for a time before taking on socket.io as well, otherwise you're trying to learn a whole heap of technologies all at once is quite a lot to try and take on board all at once.
I want to extend this open topic: Add Routes at Runtime (ExpressJs) which sadly didn't help me enough.
I'm working on an application that allows the creation of different API's that runs on NodeJs. The UI looks like this:
As you can see, this piece of code contains two endpoints (GET, POST) and as soon as I press "Save", it creates a .js file located in a path where the Nodejs application is looking for its endpoints (e.g: myProject\dynamicRoutes\rule_test.js).
The problem that I have is that being that the Nodejs server is running while I'm developing the code, I'm not able to invoke these new endpoints unless I restart the server once again (and ExpressJs detects the file).
Is there a way to register new routes while the
NodeJs (ExpressJs) is running?
I tried to do the following things with no luck:
app.js
This works if the server is restarted. I tried to include this library (express-dynamic-router, but not working at runtime.)
//this is dynamic routing function
function handleDynamicRoutes(req,res,next) {
var path = req.path; //http://localhost:8080/api/rule_test
//LoadModules(path)
var controllerPath = path.replace("/api/", "./dynamicRoutes/");
var dynamicController = require(controllerPath);
dynamicRouter.index(dynamicController[req.method]).register(app);
dynamicController[req.method] = function(req, res) {
//invocation
}
next();
}
app.all('*', handleDynamicRoutes);
Finally, I readed this article (#NodeJS / #ExpressJS: Adding routes dynamically at runtime), but I couldn't figure out how this can help me.
I believe that this could be possible somehow, but I feel a bit lost. Anyone knows how can I achieve this? I'm getting a CANNOT GET error, after each file creation.
Disclaimer: please know that it is considered as bad design in terms of stability and security to allow the user or even administrator to inject executable code via web forms. Treat this thread as academic discussion and don't use this code in production!
Look at this simple example which adds new route in runtime:
app.get('/subpage', (req, res) => res.send('Hello subpage'))
So basically new route is being registered when app.get is called, no need to walk through routes directory.
All you need to do is simply load your newly created module and pass your app to module.exports function to register new routes. I guess this one-liner should work just fine (not tested):
require('path/to/new/module')(app)
Is req.params enough for you?
app.get('/basebath/:path, (req,res) => {
const content = require('content/' + req.params.path);
res.send(content);
});
So the user can enter whatever after /basepath, for example
http://www.mywebsite.com/basepath/bergur
The router would then try to get the file content/bergur.js
and send it's contents.
I'm starting with NodeJS and Express 4, and I'm a bit confused. I been reading the Express website, but can't see when to use a route handler or when to use express.Router.
As I could see, if I want to show a page or something when the user hits /show for example I should use:
var express = require('express')
var app = express()
app.get("/show", someFunction)
At the beginning, I thought this was old (for Express 3). Is that right or this is the way for Express 4 too?
If this is the way to do it in Express 4, what is express.Router used for?
I read almost the same example as above but using express.Router:
var express = require('express');
var router = express.Router();
router.get("/show", someFunction)
So, what's the difference between both examples?
Which one should I use if I just want to do a simple testing website?
app.js
var express = require('express'),
dogs = require('./routes/dogs'),
cats = require('./routes/cats'),
birds = require('./routes/birds');
var app = express();
app.use('/dogs', dogs);
app.use('/cats', cats);
app.use('/birds', birds);
app.listen(3000);
dogs.js
var express = require('express');
var router = express.Router();
router.get('/', function(req, res) {
res.send('GET handler for /dogs route.');
});
router.post('/', function(req, res) {
res.send('POST handler for /dogs route.');
});
module.exports = router;
When var app = express() is called, an app object is returned. Think of this as the main app.
When var router = express.Router() is called, a slightly different mini app is returned. The idea behind the mini app is that each route in your app can become quite complicated, and you'd benefit from moving all that code into a separate file. Each file's router becomes a mini app, which has a very similar structure to the main app.
In the example above, the code for the /dogs route has been moved into its own file so it doesn't clutter up the main app. The code for /cats and /birds would be structured similarly in their own files. By separating this code into three mini apps, you can work on the logic for each one in isolation, and not worry about how it will affect the other two.
If you have code (middleware) that pertains to all three routes, you can put it in the main app, before the app.use(...) calls. If you have code (middleware) that pertains to just one of those routes, you can put it in the file for that route only.
Express 4.0 comes with the new Router. As mentioned on the site:
The express.Router class can be used to create modular mountable route
handlers. A Router instance is a complete middleware and routing
system; for this reason it is often referred to as a “mini-app”.
There is a good article at https://scotch.io/tutorials/learn-to-use-the-new-router-in-expressjs-4 which describes the differences and what can be done with routers.
To summarize
With routers you can modularize your code more easily. You can use routers as:
Basic Routes: Home, About
Route Middleware to log requests to the console
Route with Parameters
Route Middleware for Parameters to validate specific parameters
Validates a parameter passed to a certain route
Note:
The app.router object, which was removed in Express 4, has made a comeback in Express 5. In the new version, it is a just a reference to the base Express router, unlike in Express 3, where an app had to explicitly load it.
How they are different
Everyone, including the documentation, tends to refer back to how much they are the same, but not actually reference any differences. Well, they are, in fact, different.
var bigApp = express();
var miniApp = express.Router();
listen()
The most obviously difference is that the bigApp will give listen, which just a rather confusing way to do what would otherwise be simple and obvious the node http or https module:
var server = require('http').createServer(bigApp);
server.listen(8080, function () {
console.info(server.address());
});
I consider this an anti-pattern because it abstracts and obscures away something that wasn't complicated or difficult in the first place, and then makes it difficult for people to use websockets and other middleware that require the raw http server.
Internal State
The big difference, which is really important, is that all bigApps have separate internal state.
bigApp.enable('trust proxy');
bigApp.enabled('trust proxy');
// true
var bigApp2 = express();
bigApp2.enabled('trust proxy');
// false
bigApp.use('/bunnies', bigApp2);
// WRONG! '/bunnies' will NOT trust proxies
A miniApp passed to a bigApp, however, will be operated by the bigApp in such a way that its internal state and thisness will be preserved and those routes will behave accordingly.
bigApp.enable('trust proxy');
bigApp.enabled('trust proxy');
// true
var miniApp = express.Router();
bigApp.use('/bunnies', miniApp);
// CORRECT! All state and such are preserved
This can be a big deal because express does a lot of (sometimes trixy) things to the http.ServerRequest and httpServerResponse object - such as modifying (or hijacking) req.url and req.originalUrl and various other properties you've been using without realizing - and you probably don't want that duplicated and separated.
Smaller API
There is a smaller, more well-defined number of functions a Router can use:
.use(mount, fn)
.all(mount, fn)
.options(mount, fn)
.head(mount, fn)
.get(mount, fn)
.post(mount, fn)
.patch(mount, fn)
.put(mount, fn)
.delete(mount, fn)
.route(mount).XXXX
.param(name, cb).XXXX
There are a few other convenience methods as well, such as basic(), but you won't find set() or enable() or other methods that change the larger app state.
app.route('/book')
.get(function (req, res) {
res.send('Get a random book')
})
.post(function (req, res) {
res.send('Post a random book')
})
As in above example, we can add different HTTP request method under a route.
Let’s say your application is little complex. So what we do first is we divide the application into multiple modules so that changes in one module doesn't clutter the others and you can keep working on individual modules, but at the end of the day you need to integrate everything into one since you are building a single application. It is like we have one main application and few child applications whose parent is the main application.
So when we create the parent application we create one using
const express = require("express");
const parent = express();
And to this parent application we need to bring in the child applications. But since the child applications are not totally different applications (since they run in the same context - java term), express provides the way to do it by means on the Express's Router function and this is what we do in the each child module file and lets call one such child module as aboutme.
const express = require("express");
export const router = express.Router();
By export we are making this module available for other to consume and since we have modularized things we need to make the module files available to the parent application by means of node's require function just like any other third party modules and the parent file looks something like this:
const express = require("express");
const parent = express();
const child = require("./aboutme");
After we make this child module available to the parent, we need to tell the parent application when to use this child application. Lets say when a user hits the path aboutme we need the child application about me to handle the request and we do it by using the Express's use method:
parent.use("/aboutme", child);
and in one shot the parent file looks like this:
const express = require("express");
const parent = express();
const child = require("./aboutme");
parent.use("/aboutme", child);
Above all what the parent can do is it can start a server where as the child cannot. Hope this clarifies. For more information you can always look at the source code which takes some time but it gives you a lot of information.
using app.js to write routes means that they are accessible to all the users as app.js is loaded on application start. However, putting routes in express.router() mini apps protect and restrict their accessibility.
In a word , express.Routercan do more things when compares to app.get(),such as middleware, moreover, you can define one more router object with express.Router()
express.Router has many options:
enable case sensitivity: /show route to not be the same as /Show, this behavior is disabled by default
strict routing mode: /show/ route to not the same as /show, this behavior is also disabled by default
we can add specific middleware/s to specific routes
In one of the questions in the quiz this was asked: "express.Router() creates an object that behaves similar to the app object."
The correct answer is 'True'. I know that we can both create routers by using either of the two but is it safe to say that they are not the same in all cases? If my understanding is correct, the express() variable can do more things like start a server while the other one cannot.
In a complicated application, app is module, for example article and user. router is controller or action in module, for example article create and list.
E.g the url https://example.com/article/create parse article module and create router.
also app and router can be level-in-level.
Here are three pieces of terminology used in documentation relating to ConnectJS for NodeJS that keeps getting used, but that I don't completely undertand:
1) views and controllers
2) partials and collections
3) Middleware
Let's start from the bottom up.
Level 0: built-in http module
In the beginning, there is node.js's built-in http.Server written by Ryan Dahl. You write a function(req, res), and Node will call your function each time a new connection is accepted:
// Hello world HTTP server using http module:
var http = require('http');
var app = http.createServer(function (req, res) {
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello, world.');
});
app.listen(8080, '127.0.0.1');
Level 1: Connect
Connect, written by Tim Caswell, is simply a subclass of http.Server that makes it easier to organize your code. Instead of writing a single callback that handles every request, you chain together some middleware. Each middleware is a function(req, res, next) that handles the request if possible, or calls next(error) if it did not finish handling the user's request. The middleware handlers are called in the order of their use; you should call the catch-all app.use(connect.errorHandler()) at the end.
One important middleware is the router, which allows you to filter some middleware based on a pattern of the URL path. The syntax for the route patterns is based on ruby's Sinatra routes. When I use the filter /hello/:name, req.params.name will be set to the matching part of the URL.
var connect = require('connect');
var app = connect.createServer();
app.use(connect.favicon());
app.use(connect.logger());,
app.use(connect.router(function(app) {
app.get('/hello/:name', function(req, res, next) {
try {
if (Math.random() > 0.5) {
throw new Error('Random error!');
}
res.writeHead(200, {'Content-Type': 'text/plain'});
res.end('Hello, ' + req.params.name);
} catch (e) {
return next(e);
}
});
}));
app.listen(8080, '127.0.0.1');
In Connect, every handler is middleware! You use whichever functionality you need like bodyParser or cookieParser, and your own business logic is also a middleware function with the same signature function(req, res, next). The connect homepage gives a list of the built-in middleware.
Level 2: Express.js
Express's http server, written by TJ Holowaychuk, is in turn a subclass of Connect that forces the Sinatra style more. In Connect, there was no magic you didn't ask for, but in Express, the router and qs parser (which sets req.query) are automatically used. The router syntax is cleaned up; you call app.get, app.post, etc. directly (and the router is positioned at the first call) rather than putting them inside a function.
Express also contains many other well-documented features and helper functions to extend app, req, and res.
One feature of Express is res.render, which renders the given template file (relative to app.set('views') or $PWD/views) using the template engine implied by the extension, and res.partial, which calls render on each element of a collection (which is just any arraylike object). But I haven't used this optional feature; if you don't care for express's templates you can just res.send data yourself.
Here are some comments. If you have more specific questions, we can try to address them.
1) views and controllers
Views just means a template that can be used to render a response, which is usually HTML but could be plain text or some other format. There are many different templating syntaxes and systems out there. Some work in NodeJS as well as in web browsers. That's all there is to views.
Controllers are the "C" in the MVC design pattern and are responsible as an intermediary between views and models. They are basically the glue that handles some basic things like formatting choices that don't belong in the model code.
2) partials and collections
(Side comment, these are really part of Express.js, not Connect, but they are sibling libraries)
Partials is a document template representing a small portion or snippet of a document, as opposed to a complete HTML document. Partials can be included by other templates and are often re-used by multiple containing templates. Collections go hand in hand with them. For example, you might have a partial to display a "President" object and in that partial you'd have markup for a photo, dates he served as president, political party, etc. You could use that same partial throughout your site whenever you wanted to display a "President" record/object. If you had a collection of several "President" objects, "collections" give you an easy way to say "render a president partial for each president object in this list".
3) middleware
The way connect handles responding to HTTP requests is to route the request through a series of functions called middleware. Each middleware function adheres to a basic API of (req, res, next) and a few behavioral requirements. Each piece of middleware can do one specific bit of processing, then when it's done, call next() to tell connect to move on to the next middleware function in the chain. Connect comes with a bunch of middleware modules which you can see on github. Middleware can do whatever it wants. For example, parse JSON request bodies, search the filesystem for a matching static file to serve, check for session cookies, log to a log file, and so on. This design makes it really easy to re-use code as well as to combine separate middleware functions in novel combinations. Some middleware functions deal with parsing and processing the request, some deal with generating the response. Typically you can find existing middleware functions that do a lot of request processing (parsing, logging, decoding, converting, etc), and you provide your own middleware to actually render the response, which is also usually the last middleware in the chain.