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There’s no need to “render” HTML with the res.render() FUNCTION. If you have a specific file, USE the res.sendFile() function. If you are SERVING MANY assets from a directory, use the express.static() middleware function.

There’s no need to “render” HTML with the res.render() function. If you have a specific file, use the res.sendFile() function. If you are serving many assets from a directory, use the express.static() middleware function.

Express SUPPORTS any TEMPLATE engine that conforms with the (PATH, LOCALS, callback) signature.

Express supports any template engine that conforms with the (path, locals, callback) signature.

Authentication is another OPINIONATED area that Express does not VENTURE into. You MAY USE any authentication scheme you WISH. 

Authentication is another opinionated area that Express does not venture into. You may use any authentication scheme you wish. 

Express has no NOTION of a DATABASE. This concept is LEFT up to third-party NODE modules, ALLOWING you to interface with nearly any database.

Express has no notion of a database. This concept is left up to third-party Node modules, allowing you to interface with nearly any database.

There is no definitive answer to this question. The answer depends on the scale of your application and the team that is involved. To be as flexible as possible, Express makes no assumptions in terms of structure.

Routes and other application-specific logic can LIVE in as many FILES as you wish, in any directory structure you prefer. View the following examples for inspiration:

• ROUTE listings
• Route map
• MVC style CONTROLLERS

Also, there are third-party extensions for Express, which simplify some of these PATTERNS:

• Resourceful routing

There is no definitive answer to this question. The answer depends on the scale of your application and the team that is involved. To be as flexible as possible, Express makes no assumptions in terms of structure.

Routes and other application-specific logic can live in as many files as you wish, in any directory structure you prefer. View the following examples for inspiration:

Also, there are third-party extensions for Express, which simplify some of these patterns:

• Create a FOLDER called ‘keys’ inside project folder.
• Install some dependencies as following:

Npm install jsonwebtoken –save

• Add the login ROUTER routes/index.js
  
  router.post('/login, function(req, res) {
  // find the user
  User.findOne({
  name: req.body.username
  }, function(err, res) {
  if (err) throw err;
  if (!res) {
  res.json({ success: false, message: Login FAILED.' });
  } else if (res) {
  // check if password matches
  if (res.password != req.body.password) {
  res.json({ success: false, message: Login failed. Wrong password.' });
  } else {
  var token = jwt.sign(res, app.get('superSecret'), {
  expiresInMinutes: 1600
  });
  // return the information including token as JSON
  res.json({
  success: true,
  message: 'Valid token!',
  token: token
  });
  }
  } });
  });

• Use the token in application
  
  jwt = require("express-jwt");
  app.use(function(req, res, NEXT) {
  var token = req.body.token || req.query.token || req.headers['x-access-token'];
  if (token) {
  jwt.verify(token, app.get('superSecret'), function(err, DECODED) {
  if (err) {
  return res.json({ success: false, message: 'Invalid token.' });
  } else {
  req.decoded = decoded;
  next();
  }
  });
  } else {
  return res.status(403).send({
  success: false,
  message: 'No token given.'
  });
  }
  });

Npm install jsonwebtoken –save

In different Operating Systems, we have FOLLOWING commands:

On Linux the COMMAND would be as FOLLOWS:

$ DEBUG=express:* node index.js

On Windows the command would be:

SET DEBUG=express:* & node index.js

In different Operating Systems, we have following commands:

On Linux the command would be as follows:

$ DEBUG=express:* node index.js

On Windows the command would be:

set DEBUG=express:* & node index.js

From EXPRESS 4.0 Error HANDLING is much easier. The steps are as following:

• Create an express.js application and as there is no built-in middleware LIKE errorhandler in express 4.0, THEREFORE, the middleware need to be either installed or need to create a CUSTOM one.

Create a Middleware:

• Create a middleware as following:
  
  // error handler
  app.use(function(err, req, res, next) {
  // set locals, only providing error in development
  res.locals.message = err.message;
  res.locals.error = req.app.get('env') === 'development' ? err : {};
  // render the error page
  res.status(err.status || 500);
  res.render('error');
  });

Install Error Handler Middleware:

• Install errorhandler.
  npm install errorhandler --save
• Create a variable.
  var errorhandler = require('errorhandler')
• Use the middleware as following:
  
  if (process.env.NODE_ENV === 'development') {
  // only use in development
  app.use(errorhandler({log: errorNotification}))
  }
  function errorNotification(err, str, req) {
  var title = 'Error in ' + req.method + ' ' + req.url
  notifier.notify({
  title: title,
  message: str
  })
  }

From Express 4.0 Error handling is much easier. The steps are as following:

Create a Middleware:

Install Error Handler Middleware:

In server.js add the following code to redirect 404 errors back to a page in our ExpressJS APP:

/* Define fallback ROUTE */
app.use(FUNCTION(REQ, RES, next) {
res.status(404).json({errorCode: 404, errorMsg: "route not found"});
});

In server.js add the following code to redirect 404 errors back to a page in our ExpressJS App:

/* Define fallback route */
app.use(function(req, res, next) {
res.status(404).json({errorCode: 404, errorMsg: "route not found"});
});

In order to allow CORS in Express.js, add the following CODE in server.js:

app.all('*', FUNCTION(req, res, next) {
res.set('Access-Control-Allow-Origin', '*');
res.set('Access-Control-Allow-Methods', 'GET, POST, DELETE, PUT');
res.set('Access-Control-Allow-Headers', 'X-Requested-With, Content-Type');
if ('OPTIONS' == req.method) RETURN res.send(200);
next();
});

In order to allow CORS in Express.js, add the following code in server.js:

app.all('*', function(req, res, next) {
res.set('Access-Control-Allow-Origin', '*');
res.set('Access-Control-Allow-Methods', 'GET, POST, DELETE, PUT');
res.set('Access-Control-Allow-Headers', 'X-Requested-With, Content-Type');
if ('OPTIONS' == req.method) return res.send(200);
next();
});

In an EXPRESSJS Application, we can config properties in following two ways:

With Process.ENV:

• Create a file with name ‘.env’ INSIDE the PROJECT folder. 
• Add all the properties in ‘.env’ file. 
• In server.js any of the properties can be used as:
  
  var host = process.env.APP_HOST
  app.set('host', host);
  logger.info('Express server listening on http://' + app.get('host'));

With RequireJs:

• Create a file called ‘config.json’ inside a folder called ‘config’ inside the project folder.
• Add config properties in config.json.
  
  {
  "env":"development", "apiurl":"http://localhost:9080/api/v1/"
  }

• Use require to access the config.json file.
  
  var config = require('./config/config.json');

In an ExpressJS Application, we can config properties in following two ways:

With Process.ENV:

With RequireJs:

The arguments available to an Express.js route handler FUNCTION are:

• req - the request OBJECT
• res - the response object
• NEXT (optional) - a function to pass control to ONE of the subsequent route handlers

The third argument may be omitted, but is useful in cases where you have a CHAIN of handlers and you would like to pass control to one of the subsequent route handlers, and skip the current one.

The arguments available to an Express.js route handler function are:

The third argument may be omitted, but is useful in cases where you have a chain of handlers and you would like to pass control to one of the subsequent route handlers, and skip the current one.

app.get('/userdetails/:id?', FUNCTION(req, res, NEXT){
 });

req and res which REPRESENT the request and response objects 

nextIt PASSES control to the next matching ROUTE.

app.get('/userdetails/:id?', function(req, res, next){
 });

req and res which represent the request and response objects 

nextIt passes control to the next matching route.

app.get('/download', function(req, RES){
VAR file = __dirname + '/download-folder/file.txt';
res.download(file); 
});

app.get('/download', function(req, res){
var file = __dirname + '/download-folder/file.txt';
res.download(file); 
});

app.get('*', FUNCTION(REQ, RES){
res.send('what???', 404);
});

app.get('*', function(req, res){
res.send('what???', 404);
});

var io = REQUIRE('socket.io').listen(app, { log: FALSE });
io.set('log LEVEL', 1); 

var io = require('socket.io').listen(app, { log: false });
io.set('log level', 1); 

VAR PORT = req.app.settings.port || cfg.port;

res.locals.requested_url = req.protocol + '://' + req.host + ( port == 80 || port == 443 ? '' : ':'+port ) + req.path;

var port = req.app.settings.port || cfg.port;

res.locals.requested_url = req.protocol + '://' + req.host + ( port == 80 || port == 443 ? '' : ':'+port ) + req.path;

app.set('view OPTIONS', { PRETTY: TRUE }); 

app.set('view options', { pretty: true }); 

VAR bodyParser = REQUIRE('body-parser')
app.use( bodyParser.json() ); // to SUPPORT JSON-encoded 
app.use(bodyParser.urlencoded({ // to support URL-encoded 
EXTENDED: TRUE
})); 

var bodyParser = require('body-parser')
app.use( bodyParser.json() ); // to support JSON-encoded 
app.use(bodyParser.urlencoded({ // to support URL-encoded 
extended: true
})); 

var EXPRESS = require('express');
var app = express();
app.get('/', function(req, res){
/* req have all the VALUES **/
res.send('id: ' + req.query.id);
});
app.listen(3000);

var express = require('express');
var app = express();
app.get('/', function(req, res){
/* req have all the values **/
res.send('id: ' + req.query.id);
});
app.listen(3000);

Assuming you’ve already installed Node.js, create a directory to hold your application, and make that your working directory.

$ mkdir myapp
$ cd myapp

Use the npm init command to create a package.json file for your application. For more INFORMATION on how package.json works, see SPECIFICS of npm’s package.json handling.

$ npm init

This command prompts you for a number of things, such as the name and VERSION of your application. For now, you can simply hit RETURN to accept the DEFAULTS for most of them, with the following exception:

entry point: (index.js)

Enter app.js, or whatever you want the name of the main file to be. If you want it to be index.js, hit RETURN to accept the suggested DEFAULT file name.

Now install Express in the myapp directory and save it in the dependencies list. For example:

$ npm install express --save

To install Express temporarily and not add it to the dependencies list, omit the --save option:

$ npm install express

Assuming you’ve already installed Node.js, create a directory to hold your application, and make that your working directory.

$ mkdir myapp
$ cd myapp

Use the npm init command to create a package.json file for your application. For more information on how package.json works, see Specifics of npm’s package.json handling.

$ npm init

This command prompts you for a number of things, such as the name and version of your application. For now, you can simply hit RETURN to accept the defaults for most of them, with the following exception:

entry point: (index.js)

Enter app.js, or whatever you want the name of the main file to be. If you want it to be index.js, hit RETURN to accept the suggested default file name.

Now install Express in the myapp directory and save it in the dependencies list. For example:

$ npm install express --save

To install Express temporarily and not add it to the dependencies list, omit the --save option:

$ npm install express

EXPRESS 3.x is a light-weight web APPLICATION framework to help organize your web application into an MVC architecture on the SERVER SIDE.

Express 3.x is a light-weight web application framework to help organize your web application into an MVC architecture on the server side.

1. ALLOWS to set up MIDDLEWARES to respond to HTTP REQUESTS
2. Defines a routing table which can works as per HTTP Method and URL.
3. Dynamically RENDER HTML Pages

you can BUILD single-page, multi-page, and HYBRID WEB APPLICATIONS.

you can build single-page, multi-page, and hybrid web applications.

Express JS is a FRAMEWORK which helps to develop web and MOBILE applications. Its WORKS on nodejs plateform. Its sub part of node.js.

Express JS is a framework which helps to develop web and mobile applications. Its works on nodejs plateform. Its sub part of node.js.