Updated April 3, 2023
Introduction Express JS Interview Questions And Answers
Express.js is a free and open supply software system and internet application framework for Node JS that was designed for the event of internet applications and API’s. It’s additionally the quality server framework for Node JS. It is developed by TJ Holowaychuk on 16th November 2010. At the side of the MongoDB info and Angular JS frontend framework, Express JS is that the backend a part of the MEAN stack. With the assistance of this, you’ll be able to manage everything from routes to handling requests and views. It even provides a sturdy set of options for numerous internet and mobile applications.
Let’s see a number of the core options of Express JS framework:
- It will be accustomed to style a single-page, multi-page and hybrid internet application.
- It permits to set up middle ware’s to retort to HTTP Requests.
- It defines a routing table that is employed to perform completely different actions supported HTTP technique and address.
- It permits to dynamically render HTML Pages supported passing arguments to templates.
- It is Ultra-fast I/O
- It is an Asynchronous and single rib
- It has MVC like structure
- It is strong API makes routing simple
So if you have finally found your dream job in Express JS but are wondering how to crack the 2023 Express JS Interview and what could be the probable Express JS Interview Questions. Every interview is different and the scope of a job is different too. Keeping this in mind we have designed the most common Express JS Interview Questions and answers to help you get success in your interview.
Below are the highest rated Express JS Interview Questions queries that are largely asked in an interview. These high rated questions are divided into two parts which are as follows:
Part 1 – Express JS Interview Questions (Basic)
This first part covers basic Express JS Interview Questions and answers
1. What do you mean by Express JS and what is its use?
Answer:
Express JS is an application framework that is light-weighted node JS. Variety of versatile, helpful and vital options are provided by this JavaScript framework for the event of mobile additionally as internet applications with the assistance of node JS.
Express JS Use – Express.js could be a light-weight internet application that helps in organizing the net application into MVC design on the server aspect.
2. Write the steps for setting up an Express JS application?
Answer:
Following are the steps accustomed for An Express JS application:
- A folder with a constant name because the project name is made.
- A file named package.json is made within the folder created.
- “npm install” command is run on the electronic communication. It installs all the libraries gift in package.json.
- A file named server.js is made.
- “Router” file is made within the package that consists of a folder named index.js.
- “App” is made within the package that has the index.html file.
Let us move on to the next Express JS Interview Questions
3. What function are arguments available to Express JS route handlers?
Answer:
The arguments which are available to an Express JS route handler-function are-
- Req: the request object
- Res: the response object
- Next (optional): a function that is employed to pass management to 1 of the following route handlers.
The third argument is optional and should be omitted, however, in some cases, it’s helpful wherever there’s a series of handlers and management will be passed to 1 of the following route handlers skipping this one.
4. How to Config properties in Express JS?
Answer:
In Express JS, there are 2 ways that for configuring the properties:
With process.ENV:
- A file with the name “.env” is to be created within the project folder.
- All the properties are to be other within the “.env” file.
- Any of the properties will be employed in server.js.
With require.JS:
- A file with the name “config.json” is to be created within the config folder within the project folder.
- The config properties are to be present within the config.json file.
- Now, ought to be accustomed access the config.json file.
5. How Should I Structure my Express JS Application?
Answer:
This is the basic Express JS Interview Questions asked in an interview. There is no definitive answer to the current question. The solution depends on the dimensions of your application and therefore the team that’s concerned.
Routes and alternative application-Express logic will board as several files as you would like, in any directory structure you favor. Read the subsequent examples for inspiration:
- Route listings
- Route map
- MVC vogue controllers
Also, there are third-party extensions for Express JS applications that modify a number of these patterns:
- Resourceful routing
Part 2 – Express JS Interview Questions (Advanced)
Let us now have a look at the advanced Express JS Interview Questions.
6. How to allow CORS in Express JS? Explain with an example?
Answer:
In order to permit CORS in Express.js, add the subsequent code in server.js:
For Example:
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();
});7. How to enable debugging in express app?
Answer:
In different operative Systems, we’ve got following commands:
On UNIX operating system the command would be as follows:
$ DEBUG=express:* node index.jsOn Windows the command would be:
set DEBUG=express:* & node index.jsFrom Webstrome IDE
C:\Program Files (x86)\JetBrains\WebStorm 2016.2.4\bin\runnerw.exe" "C:\Program Files\nodejs\node.exe" --debug-brk=61081 --expose_debug_as=v8debug E:\Development\nodejd\librarey\bin\wwwLet us move on to the next advanced Express JS Interview Questions.
8. Explain Error Handling In Express.js Using An Example?
Answer:
From Express 4.0 Error handling is easier. The steps are as following:
Create a middleware as following:
// error handler
app.use(function(err, req, res, next) solely 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 e errorhandler = require('errorhandler')- Use the middleware as following:
if (process.env.NODE_ENV === 'development') solely use in development
app.use(errorhandler())
}
function errorNotification(err, str, req) power unit title = 'Error in ' + req.method + ' ' + req.url
notifier.notify()
}9. What is the use of next in Express JS?
Answer:
Next -It passes management to a consecutive matching route. OR a operate to pass management to 1 of the following route handlers.
The argument could also be omitted, however, is beneficial in cases wherever you have got a series of handlers and you’d wish to pass management to 1 of the following route handlers, and skip this one.
app.get('/user details/:id?', function(req, res, next));- Req and Res: It represents the request and response objects
- Next: It passes management to a consecutive matching route.
10. How to Redirect 404 Errors to A Page In ExpressJS?
Answer:
In server.js add the subsequent code to send 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"});
});Recommended Articles
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