Despite knowing JavaScript quite well, I'm confused what exactly these three projects in Node.js ecosystem do. Is it something like Rails' Rack? Can someone please explain?
[Update: As of its 4.0 release, Express no longer uses Connect. However, Express is still compatible with middleware written for Connect. My original answer is below.]
I'm glad you asked about this, because it's definitely a common point of confusion for folks looking at Node.js. Here's my best shot at explaining it:
Node.js itself offers an http module, whose createServer method returns an object that you can use to respond to HTTP requests. That object inherits the http.Server prototype.
Connect also offers a createServer method, which returns an object that inherits an extended version of http.Server. Connect's extensions are mainly there to make it easy to plug in middleware. That's why Connect describes itself as a "middleware framework," and is often analogized to Ruby's Rack.
Express does to Connect what Connect does to the http module: It offers a createServer method that extends Connect's Server prototype. So all of the functionality of Connect is there, plus view rendering and a handy DSL for describing routes. Ruby's Sinatra is a good analogy.
Then there are other frameworks that go even further and extend Express! Zappa, for instance, which integrates support for CoffeeScript, server-side jQuery, and testing.
Here's a concrete example of what's meant by "middleware": Out of the box, none of the above serves static files for you. But just throw in connect.static (a middleware that comes with Connect), configured to point to a directory, and your server will provide access to the files in that directory. Note that Express provides Connect's middlewares also; express.static is the same as connect.static. (Both were known as staticProvider until recently.)
My impression is that most "real" Node.js apps are being developed with Express these days; the features it adds are extremely useful, and all of the lower-level functionality is still there if you want it.
The accepted answer is really old (and now wrong). Here's the information (with source) based on the current version of Connect (3.0) / Express (4.0).
What Node.js comes with
http / https createServer which simply takes a callback(req,res) e.g.
var server = http.createServer(function (request, response) {
// respond
response.write('hello client!');
response.end();
});
server.listen(3000);
What connect adds
Middleware is basically any software that sits between your application code and some low level API. Connect extends the built-in HTTP server functionality and adds a plugin framework. The plugins act as middleware and hence connect is a middleware framework
The way it does that is pretty simple (and in fact the code is really short!). As soon as you call var connect = require('connect'); var app = connect(); you get a function app that can:
Can handle a request and return a response. This is because you basically get this function
Has a member function .use (source) to manage plugins (that comes from here because of this simple line of code).
Because of 1.) you can do the following :
var app = connect();
// Register with http
http.createServer(app)
.listen(3000);
Combine with 2.) and you get:
var connect = require('connect');
// Create a connect dispatcher
var app = connect()
// register a middleware
.use(function (req, res, next) { next(); });
// Register with http
http.createServer(app)
.listen(3000);
Connect provides a utility function to register itself with http so that you don't need to make the call to http.createServer(app). Its called listen and the code simply creates a new http server, register's connect as the callback and forwards the arguments to http.listen. From source
app.listen = function(){
var server = http.createServer(this);
return server.listen.apply(server, arguments);
};
So, you can do:
var connect = require('connect');
// Create a connect dispatcher and register with http
var app = connect()
.listen(3000);
console.log('server running on port 3000');
It's still your good old http.createServer with a plugin framework on top.
What ExpressJS adds
ExpressJS and connect are parallel projects. Connect is just a middleware framework, with a nice use function. Express does not depend on Connect (see package.json). However it does the everything that connect does i.e:
Can be registered with createServer like connect since it too is just a function that can take a req/res pair (source).
A use function to register middleware.
A utility listen function to register itself with http
In addition to what connect provides (which express duplicates), it has a bunch of more features. e.g.
Has view engine support.
Has top level verbs (get/post etc.) for its router.
Has application settings support.
The middleware is shared
The use function of ExpressJS and connect is compatible and therefore the middleware is shared. Both are middleware frameworks, express just has more than a simple middleware framework.
Which one should you use?
My opinion: you are informed enough ^based on above^ to make your own choice.
Use http.createServer if you are creating something like connect / expressjs from scratch.
Use connect if you are authoring middleware, testing protocols etc. since it is a nice abstraction on top of http.createServer
Use ExpressJS if you are authoring websites.
Most people should just use ExpressJS.
What's wrong about the accepted answer
These might have been true as some point in time, but wrong now:
that inherits an extended version of http.Server
Wrong. It doesn't extend it and as you have seen ... uses it
Express does to Connect what Connect does to the http module
Express 4.0 doesn't even depend on connect. see the current package.json dependencies section
node.js
Node.js is a javascript motor for the server side.
In addition to all the js capabilities, it includes networking capabilities (like HTTP), and access to the file system.
This is different from client-side js where the networking tasks are monopolized by the browser, and access to the file system is forbidden for security reasons.
node.js as a web server: express
Something that runs in the server, understands HTTP and can access files sounds like a web server. But it isn't one.
To make node.js behave like a web server one has to program it: handle the incoming HTTP requests and provide the appropriate responses.
This is what Express does: it's the implementation of a web server in js.
Thus, implementing a web site is like configuring Express routes, and programming the site's specific features.
Middleware and Connect
Serving pages involves a number of tasks. Many of those tasks are well known and very common, so node's Connect module (one of the many modules available to run under node) implements those tasks.
See the current impressing offering:
logger request logger with custom format support
csrf Cross-site request forgery protection
compress Gzip compression middleware
basicAuth basic http authentication
bodyParser extensible request body parser
json application/json parser
urlencoded application/x-www-form-urlencoded parser
multipart multipart/form-data parser
timeout request timeouts
cookieParser cookie parser
session session management support with bundled MemoryStore
cookieSession cookie-based session support
methodOverride faux HTTP method support
responseTime calculates response-time and exposes via X-Response-Time
staticCache memory cache layer for the static() middleware
static streaming static file server supporting Range and more
directory directory listing middleware
vhost virtual host sub-domain mapping middleware
favicon efficient favicon server (with default icon)
limit limit the bytesize of request bodies
query automatic querystring parser, populating req.query
errorHandler flexible error handler
Connect is the framework and through it you can pick the (sub)modules you need.
The Contrib Middleware page enumerates a long list of additional middlewares.
Express itself comes with the most common Connect middlewares.
What to do?
Install node.js.
Node comes with npm, the node package manager.
The command npm install -g express will download and install express globally (check the express guide).
Running express foo in a command line (not in node) will create a ready-to-run application named foo. Change to its (newly created) directory and run it with node with the command node <appname>, then open http://localhost:3000 and see.
Now you are in.
Connect offers a "higher level" APIs for common HTTP server functionality like session management, authentication, logging and more. Express is built on top of Connect with advanced (Sinatra like) functionality.
Node.js itself offers an HTTP module, whose createServer method returns an object that you can use to respond to HTTP requests. That object inherits the http.Server prototype.
Related information, especially if you are using NTVS for working with the Visual Studio IDE. The NTVS adds both NodeJS and Express tools, scaffolding, project templates to Visual Studio 2012, 2013.
Also, the verbiage that calls ExpressJS or Connect as a "WebServer" is incorrect. You can create a basic WebServer with or without them. A basic NodeJS program can also use the http module to handle http requests, Thus becoming a rudimentary web server.
middleware as the name suggests actually middleware is sit between middle.. middle of what? middle of request and response..how request,response,express server sit in express app
in this picture you can see requests are coming from client then the express server server serves those requests.. then lets dig deeper.. actually we can divide this whole express server's whole task in to small seperate tasks like in this way.
how middleware sit between request and response small chunk of server parts doing some particular task and passed request to next one.. finally doing all the tasks response has been made..
all middle ware can access request object,response object and next function of request response cycle..
this is good example for explaining middleware in express youtube video for middleware
The stupid simple answer
Connect and Express are web servers for nodejs. Unlike Apache and IIS, they can both use the same modules, referred to as "middleware".
I am working to create a serverless REST API via Firebase Cloud Functions, which seems to work well but the examples and documentation all seem to use a monolithic solution, since they use the Express framework and essentially map the root http request to the Express app, then let it handle the routing. I understand that this is because the Firebase Hosting platform does not have the ability to handle http verbs.
My expectation was that a serverless / FaaS approach would have a function for each endpoint, making for easy updates in future since there's no need to update the whole app, just that single service - i.e. a more functional approach.
What am I missing here? Why is the approach to use a single function to contain an express app? Doesn't this defeat the purpose of a serverless / Cloud Functions approach? And is there any other way of doing this?
The documentation shows how to create an endpoint without the help of an Express app, router, or middleware:
exports.date = functions.https.onRequest((req, res) => {
// ...
});
All you have to do is arrange to send a response with res.send(...) or similar.
I've come across an interesting situation where we're using express app composition:
const rootApp = express();
const moduleOne = express();
const moduleTwo = express();
rootApp.use(moduleOne);
rootApp.use(moduleTwo);
rootApp.listen(3000);
Each of these module apps have their own routers, middleware, etc. and I was wondering what are some advantages and disadvantages of having app composition versus router composition at a higher level.
It generally allows for better isolation and use of middleware. For example I tend to roll with multiple Express Applications (composed together) when building CRUD based apps which use Single Page Web Apps (React, Ember, Angular, etc). This allows me to attach different headers to each incredibly easier.
It also makes it very easy to move each application into it's own repo, this could be useful if you later on wish to run each application as it's own service. You could then use something like nginx to route to two apps. For example:
myapp.com/api/auth -> authentication express app
myapp.com/api -> general API
myapp.com/ -> light weight express app which serves the front end.
This makes it much easier to scale your application later on, and allows more fine grained control.
In the short term, the control over various middleware is the thing I find most useful about composing express apps vs composing express routers. It means you can do "app.use()" and tends to read a lot better to other developers coming to your project.
An app is a router object with a few more properties and methods related to the overall state of your app. Properties on the app object like app.locals or methods like app.listen() apply to your whole app, not just to a set of routes. Other than that though, you can think of an app like a subclass of a router with all the capabilities of a router with added app properties.
If you look in the source code for the app object, you will see that it has a router in its instance data (not sure why they didn't actually subclass it):
this._router = new Router({...});
And, then further examination of the code shows that app.use(), app.get(), etc... all flow through that above router.
So, your app objects works just perfectly fine if all you need is one router. But, there are reasons to use more than one router. For example, if you have a series of sub-routes (say everything that starts with /api/xxx) that you want to do some authentication on, but lots of other routes don't require that auth, then you can create a router for /api, define middleware on only that router that checks your auth and then define the sub-routes on that router and you get a nice encapsulated definition of sub-routes all with their own middleware.
I have used loopback to scaffold out my application but want to use some of their components, their documentation is lacking, can I just enable the functionality I want like I would using just express?
Specifically, I want to implement OAuth2
The loopback object is directly the express object (with all the loopback sweet additions of course). You can obtain this object by requiring the server.js file scaffolded in your application.
So you can do everything express does with it, like routing for instance
var app = require('server.js').
app.get('/', function (req, res) {
res.send('Hello World!');
});
Implementing OAuth2 is absolutely possible (done it myself, without using oauth loopback plugin), nothing preventing it, but it's not exactly straightforward. I would advise to spend some time getting familiar with loopback and building a few small applications first.
I have an api written in node.js that handles calls coming in from websites, desktop applications, iOS applications etc. There are probably 50+ endpoints and each end point can accept anywhere from 1 parameter to possibly 10-20 depending on what is intendeding to be accomplished. These can be GET/POST/PUT/DEL
I want to start load testing my API and simulating users activities.
What I am looking for is suggestions on how you can capture the API call and the parameters that were passed along with it in a logical way.
I use forever to run my app and everything is written to a log file so my initial reaction was to do something like add a piece of middleware to the express routes that would capture the endpoint as well as the req.params and req.body but then I need to put this middleware in all 50+ routes kind of tedious.
Anyone done something like this before and has a good idea on how to capture calls / data with those calls as well as possibly capturing what is returned from my API.
Perhaps some module?
I need to have this in a readable format to provide to other people so they can structure a fake set of calls... so raw log files aren't really helpful unless they are outputted.... "pretty".
Thanks!
You're on the right track – just add your logger middleware via app.use, which runs the middleware on every request (rather than adding it to each route).
In fact, the Express docs give an example of using logger middleware:
var express = require('express');
var app = express();
// simple logger
app.use(function(req, res, next){
console.log('%s %s', req.method, req.url);
next();
});
Connect (on which Express is built) provides logger middleware, so you can just do:
var logFile = fs.createWriteStream('./myLogFile.log', {flags: 'a'});
app.use(express.logger({stream: logFile}));