Top 100+ Expressjs Interview Questions And Answers
Question 1. What Is Express Js?
Answer :
Express JS is a framework which facilitates to broaden web and mobile applications. Its works on nodejs plateform. Its sub part of node.Js.
Question 2. What Type Of Web Application Can Built Using Express Js?
Answer :
you can construct unmarried-page, multi-page, and hybrid net programs.
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Question 3. What Are Core Features Of Express Framework?
Answer :
Allows to installation middlewares to respond to HTTP Requests
Defines a routing desk that can works as according to HTTP Method and URL.
Dynamically render HTML Pages
Question 4. Why I Should Use Express Js?
Answer :
Express three.X is a light-weight net application framework to assist organize your net application into an MVC structure at the server facet.
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Question 5. How To Install Expressjs?
Answer :
Assuming you’ve already set up Node.Js, create a listing to hold your application, and make that your operating listing.
$ mkdir myapp
$ cd myapp
Use the npm init command to create a bundle.Json file on your application. For more records on how package deal.Json works, see Specifics of npm’s package.Json coping with.
$ npm init
This command activates you for a variety of of things, along with the call and model of your software. For now, you can genuinely hit RETURN to simply accept the defaults for maximum of them, with the subsequent exception:
access factor: (index.Js)
Enter app.Js, or whatever you need the name of the main document to be. If you need it to be index.Js, hit RETURN to simply accept the recommended default record name.
Now installation Express within the myapp listing and keep it within the dependencies list. For example:
$ npm deploy specific --store
To deploy Express quickly and not add it to the dependencies listing, omit the --shop option:
$ npm deploy explicit
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Question 6. How To Get Variables In Express.Js In Get Method?
Answer :
var explicit = require('explicit');
var app = explicit();
app.Get('/', function(req, res)
/* req have all of the values **/
res.Send('identity: ' + req.Query.Id);
);
app.Listen(3000);
Question 7. How To Get Post A Query In Express.Js?
Answer :
var bodyParser = require('body-parser')
app.Use( bodyParser.Json() ); // to guide JSON-encoded
app.Use(bodyParser.Urlencoded( // to guide URL-encoded
prolonged: true
));
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Question eight. How To Output Pretty Html In Express.Js?
Answer :
app.Set('view alternatives', pretty: real );
Question 980 port == 443 ? '' : ':'+port ) + req.Direction;
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Question 10. How To Remove Debugging From An Express App?
Answer :
var io = require('socket.Io').Concentrate(app, log: false );
io.Set('log stage', 1);
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Question 11. How To Do 404 Errors?
Answer :
app.Get('*', function(req, res)
res.Ship('what???', 404);
);
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Question 12. How To Download A File?
Answer :
app.Get('/download', function(req, res)
var record = __dirname + '/down load-folder/report.Txt';
res.Download(file);
);
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Question thirteen. What Is The Parameter “subsequent” Used For In Express?
Answer :
app.Get('/userdetails/:identification?', characteristic(req, res, subsequent)
);
req and res which represent the request and reaction gadgets
nextIt passes manipulate to the next matching course.
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Question 14. What Function Arguments Are Available To Express.Js Route Handlers?
Answer :
The arguments available to an Express.Js path handler function are:
req - the request item
res - the response item
subsequent (elective) - a feature to pass manage to one of the subsequent route handlers
The 1/3 argument may be left out, but is beneficial in cases where you have got a chain of handlers and you would love to pass manage to one of the subsequent route handlers, and skip the contemporary one.
Question 15. How To Config Properties In Express Application?
Answer :
In an ExpressJS Application, we will config houses in following two approaches:
With Process.ENV:
Create a file with name ‘.Env’ inside the task folder.
Add all of the homes in ‘.Env’ file.
In server.Js any of the homes can be used as:
var host = manner.Env.APP_HOST
app.Set('host', host);
logger.Information('Express server listening on http://' + app.Get('host'));
With RequireJs:
Create a document referred to as ‘config.Json’ inside a folder known as ‘config’ within the challenge folder.
Add config houses in config.Json.
"env":"development", "apiurl":"http://localhost:9080/api/v1/"
Use require to access the config.Json document.
Var config = require('./config/config.Json');
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Question sixteen. How To Allow Cors In Expressjs? Explain With An Example?
Answer :
In order to allow CORS in Express.Js, upload the following code in server.Js:
app.All('*', function(req, res, subsequent)
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) go back res.Send(2 hundred);
subsequent();
);
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Question 17. How To Redirect 404 Errors To A Page In Expressjs?
Answer :
In server.Js add the subsequent code to redirect 404 mistakes back to a web page in our ExpressJS App:
/* Define fallback direction */
app.Use(feature(req, res, subsequent)
res.Reputation(404).Json(errorCode: 404, errorMsg: "path now not discovered");
);
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Question 18. Explain Error Handling In Express.Js Using An Example?
Answer :
From Express 4.0 Error handling is plenty less difficult. The steps are as following:
Create an specific.Js software and as there may be no built-in middleware like errorhandler in specific 4.0, therefore, the middleware want to be either set up or want to create a custom one.
Create a Middleware:
Create a middleware as following:
// errors handler
app.Use(characteristic(err, req, res, next)
// set locals, simplest presenting blunders in development
res.Locals.Message = err.Message;
res.Locals.Error = req.App.Get('env') === 'improvement' ? Err : ;
// render the mistake page
res.Fame(err.Fame blunders');
);
Install Error Handler Middleware:
Install errorhandler.
Npm set up errorhandler --save
Create a variable.
Var errorhandler = require('errorhandler')
Use the middleware as following:
if (process.Env.NODE_ENV === 'improvement')
// handiest use in improvement
app.Use(errorhandler(log: errorNotification))
feature errorNotification(err, str, req)
var title = 'Error in ' + req.Approach + ' ' + req.Url
notifier.Notify(
identify: title,
message: str
)
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Question 19. How To Enable Debugging In Express App?
Answer :
In unique Operating Systems, we've got following instructions:
On Linux the command could be as follows:
$ DEBUG=express:* node index.Js
On Windows the command would be:
set DEBUG=explicit:* & node index.Js
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Question 20. How To Implement Jwt Authentication In Express App ? Explain With Example?
Answer :
Create a folder known as ‘keys’ inner assignment folder.
Install a few dependencies as following:
Npm set up jsonwebtoken –shop
Add the login router routes/index.Js
router.Publish('/login, characteristic(req, res)
// find the user
User.FindOne(
call: req.Body.Username
, characteristic(err, res)
if (err) throw err;
if (!Res)
res.Json( achievement: false, message: Login failed.' );
else if (res)
// test if password suits
if (res.Password != req.Frame.Password)
res.Json( fulfillment: fake, message: Login failed. Wrong password.' );
else
var token = jwt.Signal(res, app.Get('superSecret'),
expiresInMinutes: 1600
);
// go back the information together with token as JSON
res.Json(
success: actual,
message: 'Valid token!',
token: token
);
);
);
Use the token in software
jwt = require("explicit-jwt");
app.Use(characteristic(req, res, subsequent)
var token = req.Bodyquestion.Token
jwt.Affirm(token, app.Get('superSecret'), function(err, decoded)
if (err)
go back res.Json( success: false, message: 'Invalid token.' );
else
req.Decoded = decoded;
next();
);
else
return res.Reputation(403).Send(
achievement: fake,
message: 'No token given.'
);
);
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Question 21. How Should I Structure My Application?
Answer :
There is no definitive answer to this query. The solution depends on the size of your utility and the group this is involved. To be as bendy as possible, Express makes no assumptions in terms of shape.
Routes and other utility-particular common sense can stay in as many documents as you desire, in any listing structure you pick. View the subsequent examples for notion:
Route listings
Route map
MVC style controllers
Also, there are third-birthday party extensions for Express, which simplify a number of these styles:
Resourceful routing
Question 22. How Do I Define Models?
Answer :
Express has no perception of a database. This idea is left as much as 1/3-celebration Node modules, permitting you to interface with nearly any database.
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Question 23. How Can I Authenticate Users?
Answer :
Authentication is another opinionated location that Express does now not assignment into. You can also use any authentication scheme you want.
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Question 24. Which Template Engines Does Express Support?
Answer :
Express helps any template engine that conforms with the (route, locals, callback) signature.
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Question 25. How Do I Render Plain Html?
Answer :
There’s no need to “render” HTML with the res.Render() characteristic. If you have got a selected record, use the res.SendFile() characteristic. If you are serving many property from a listing, use the express.Static() middleware feature.
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