What is Express Js? What are core features of Express framework?
Express JS is a framework which helps to develop web and mobile applications. Its works on node.js plateform. Its sub part of node.js.
Express JS Features:
Following are some of the core features of Express framework ?
- Set up middlewares in order to respond to HTTP/RESTful Requests.
- It is possible to defines a routing table in order to perform different HTTP operations.
- Dynamically renders HTML Pages based on passing arguments to templates.
- Provides all the feature provides by core Node.js.
- Express prepare a thin layer, therefore, the performance is adequate.
- Organize the web application into an MVC architecture.
- Manages everything from routes to rendering view and preforming HTTP request.
What type of web application can built using Express JS?
you can build single-page, multi-page, and hybrid web applications.
What are core features of Express framework?
- Allows to set up middle-wares to respond to HTTP Requests.
- Defines a routing table which can works as per HTTP Method and URL.
- Dynamically render HTML Pages.
Why I should use Express JS?
Express 3.x is a light-weight web application framework to help organize your web application into an MVC architecture on the server side.
How to get variables in Express.js in GET Method?
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);
How to get POST a query in Express.js?
var bodyParser = require(‘body-parser’)
app.use( bodyParser.json() ); // to support JSON-encoded
app.use(bodyParser.urlencoded({ // to support URL-encoded
extended: true
}));
How to output pretty html in Express.js?
app.set(‘view options’, { pretty: true });
How to get the full url in Express?
var port = req.app.settings.port || cfg.port;
res.locals.requested_url = req.protocol + ‘://’ + req.host + ( port == 80 || port == 443 ? ” : ‘:’+port ) + req.path;
How to remove debugging from an Express app?
var io = require(‘socket.io’).listen(app, { log: false });
io.set(‘log level’, 1);
How to download a file?
app.get(‘/download’, function(req, res){
var file = __dirname + ‘/download-folder/file.txt’;
res.download(file);
});
How to 404 errors?
app.get
(‘*’, function(req, res){
res.send(‘what???’, 404);
});
What is the parameter “next” used for in Express?
app.get(‘/userdetails/:id?’, function(req, res, next){
});
Note: req and res which represent the request and response objects
nextIt passes control to the next matching route.
What Function Arguments Are Available To Express.js Route Handlers?
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.
How To Config Properties In Express Application?
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’);
How To Allow Cors In Expressjs? Explain With An Example?
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();
});
How To Redirect 404 Errors To A Page In Expressjs?
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”});
});
Explain Error Handling In Express.js Using An Example?
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
})
}
How To Enable Debugging In Express App?
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
How To Implement Jwt Authentication In Express App ? Explain With Example?
– 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.’
});
}
});
How Should I Structure My Application?
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
How Do I Define Models?
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.
How Can I Authenticate Users?
Authentication is another opinionated area that Express does not venture into. You may use any authentication scheme you wish.
Which Template Engines Does Express Support?
Express supports any template engine that conforms with the (path, locals, callback) signature.
How Do I Render Plain Html?
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.
Types of apps, where Node.js+Express.js is the right choice
- Applications, that communicate with third party resources
As we already mentioned, Node.js can handle a large amount of simultaneous connections, so it will be useful for server-side applications interacting with third-party resources and gathering data from them.
- Applications for monitoring the visitor’s actions
Node.js is a great choice for building the back-end of applications for tracking website visitors and visualizing the outcoming data. For example, you need to investigate reviews about your company as soon as they appear, keep track of all ratings and analyze them. JSSolutions has developed such project for gathering reviews from different websites in one application. We decided to build it with Node.js exactly because of the reasons, mentioned above.
- Real-time applications
Node.js allows to easily build applications that are updated in real time. Who decided to develop a real time polls application that will display voting results, updating in real time. He has chosen this technology because of its simple architecture and scalability. In addition, Node.js is an event-based and non-blocking driven server that can handle a large number of real-time users.