Node.js/express.js

Front 1

Who is the creator of Node.js and when was it initially released?

Back 1

Ryan Dahl is the creator of Node.js. The development was sponsored by Joyent and it was initially released in 2009.

Front 2

What is npm?

Back 2

npm is Node.js' package ecosystem. It is the largest ecosystem of open-source libraries in the world. It is also the name of the command line package manager used to interact with npm.

Front 3

What is the name of the file which npm uses to identify the project and its dependencies?

Back 3

Its name is package.json.

Front 4

What are the names of at least three of the most popular Node.js frameworks?

Back 4

Express, Sails, Loopback, Koa, Hapi, Meteor, etc.

Front 5

What is the name of at least one framework that utilizes Node.js for development of desktop apps?

Back 5

Electron

Front 6

What is the alternative to the Node package manager (npm), which was introduced by Facebook in 2016?

Back 6

yarn

Front 7

What is the difference between dependencies and devDependencies?

Back 7

Both are defined in the package.json. dependencies lists the packages that the project is dependent on. devDependencies lists the dependencies which are only required during testing and development.

Front 8

What is REPL and how can you access it from the command line?

Back 8

REPL stands for "Read Eval Print Loop." It is an interface for easily running Node.js code. It can be started from the command line using the node command.

Front 9

What is the name of the JavaScript engine that Node.js is built upon?

Back 9

Chrome's V8 engine.

Front 10

Does Node.js operate in a single-threaded or multi-threaded fashion?

Back 10

Node.js operates on a single thread.

Front 11

What is the event loop?

Back 11

Node.js processes incoming requests in the event loop. It is what allows Node.js to perform non-blocking operations despite the fact that JavaScript is single-threaded.

Front 12

What is Node.js' Cluster module?

Back 12

A module used to take advantage of multi-core systems, so that apps can handle more load.

Front 13

What is Node.js' Cluster module?

Back 13

A module used to take advantage of multi-core systems, so that apps can handle more load.

Front 14

Which keywords are used to export and import an object or a function from a module file?

Back 14

module.exports is used to export an object or a function. require is used to import one.

Front 15

Which keywords are used to export and import an object or a function from a module file?

Back 15

module.exports is used to export an object or a function. require is used to import one.

Front 16

Which global variable can be used to access information about the app and the environment that it runs in?

Back 16

The process variable

Front 17

What is __dirname?

Back 17

A global variable which returns the absolute path of the directory containing the currently executing file.

Front 18

What is a blocking function?

Back 18

Unlike non-blocking functions, a blocking function's execution must be completed before other statements are executed.

Front 19

Which is the first argument usually passed to a Node.js callback handler?

Back 19

It is an error object, which is null or undefined if an error did not occur.

Front 20

What does "callback hell" mean?

Back 20

Plenty of nested callbacks lead to callback hell. They make code difficult to read and maintain. One of the ways to deal with callback hell is to use the async/await syntax.

Front 21

What are async and await?

Back 21

A function marked with the async keyword can contain an await expression. The await expression pauses the execution of the function and waits for the resolution of the passed Promise. It then resumes the function's execution and returns the resolved value.

Front 22

What are async and await?

Back 22

A function marked with the async keyword can contain an await expression. The await expression pauses the execution of the function and waits for the resolution of the passed Promise. It then resumes the function's execution and returns the resolved value.

Front 23

What is the difference between setTimeout and setImmediate?

Back 23

setTimeout is used to run a function after a certain minimal timeout. setImmediate is used to run a function once the current event loop completes.

Front 24

What is the difference between setTimeout and setImmediate?

Back 24

setTimeout is used to run a function after a certain minimal timeout. setImmediate is used to run a function once the current event loop completes.

Front 25

Does the fs module, used for file-based operations, offer the possibility for synchronous or asynchronous reading and writing?

Back 25

fs offers both synchronous and asynchronous methods for reading from and writing to files.

Front 26

What are the two methods in the fs module that can be used for reading a whole file at once?

Back 26

fs.readFile and fs.readFileSync.

Front 27

What are the two methods in the fs module that can be used for reading a whole file at once?

Back 27

fs.readFile and fs.readFileSync.

Front 28

What keyword do you need to use to insert a debug breakpoint?

Back 28

The debugger keyword.

Front 29

What is an error-first callback?

Back 29

Error-first callbacks are used to pass errors and data. The first argument is always an error object that the programmer has to check if something went wrong. Additional arguments are used to pass data.

fs.readFile(filePath, function(err, data) {

if (err) {

//handle the error

}

// use the data object

});

Front 30

How can you avoid callback hells?

Back 30

To do so you have more options:

modularization: break callbacks into independent functions

use Promises

use yield with Generators and/or Promises

Front 31

How can you listen on port 80 with Node?

Back 31

You should not try to listen with Node on port 80 (in Unix-like systems) – to do so you would need superuser rights, but it is not a good idea to run your application with it.

Still, if you want to have your Node.js application listen on port 80, here is what you can do. Run the application on any port above 1024, then put a reverse proxy like nginx in front of it.

Front 32

What’s the event loop?

Back 32

Node.js runs using a single thread, at least from a Node.js developer’s point of view. Under the hood Node.js uses many threads through libuv.

Every I/O requires a callback – once they are done they are pushed onto the event loop for execution.

Front 33

What tools can be used to assure consistent style?

Back 33

JSLint by Douglas Crockford

JSHint

ESLint

JSCS

Front 34

What’s the difference between operational and programmer errors?

Back 34

Operation errors are not bugs, but problems with the system, like request timeout or hardware failure.

On the other hand programmer errors are actual bugs.

Front 35

What are the key features of Node.js?

Back 35

Asynchronous event-driven

Fast in Code execution

Single Threaded but Highly Scalable

Node.js library uses JavaScript

Front 36

Explain how do we decide, when to use Node.js and when not to use it.

Back 36

It’s ideal to use Node.js for developing streaming or event-based real-time applications that require less CPU usage such as:

Chat applications.

Game servers.

Good for collaborative environment.

Advertisement servers.

Streaming servers.

When to not use Node.js?

However, we can use Node.js for a variety of applications. But it is a single-threaded framework, so we should not use it for cases where the application requires a long processing time. If the server is doing some calculations, it won’t be able to process any other requests. Hence, Node.js is best when processing needs less dedicated CPU time.

Front 37

How to get Post Data in Node.js?

Back 37

Following is the code snippet to fetch Post Data using Node.js.

app.use(express.bodyParser());

app.post('/', function(request, response){

console.log(request.body.user);

});

Front 38

How to make a Post request in Node.js?

Back 38

The following code snippet can be used to make a Post Request in Node.js.

var request = require('request');

request.post(

'http://www.example.com/action',

{ form: { key: 'value' } },

function (error, response, body) {

if (!error && response.statusCode == 200) {

console.log(body)

}

}

);

Front 39

What is Callback in Node.js?

Back 39

We may call “callback” as an asynchronous equivalent for a function. Node.js makes heavy use of callbacks and triggers it at the completion of a given task. All the APIs of Node.js are written in such a way that they support callbacks.

For example, suppose we have a function to read a file, as soon as it starts reading the file, Node.js return the control immediately to the execution environment so that the next instruction can be executed. Once the file read operation is complete, it will call the callback function and pass the contents of the file as its arguments. Hence, there is no blocking or wait, due to File I/O. This functionality makes Node.js as highly scalable, using it processes a high number of requests without waiting for any function to return the expected result.

Front 40

How to avoid callback hell in Node.js?

Back 40

Node.js internally uses a single-threaded event loop to process queued events. But this approach may lead to blocking the entire process if there is a task running longer than expected.

Node.js addresses this problem by incorporating callbacks also known as higher-order functions. So whenever a long-running process finishes its execution, it triggers the callback associated. With this approach, it can allow the code execution to continue past the long-running task.

However, the above solution looks extremely promising. But sometimes, it could lead to complex and unreadable code. The more the no. of callbacks, the longer the chain of returning callbacks would be. Solution:

1. Make your program modular.

2. Use an async mechanism.

3. Use the promises mechanism.

4. Use generators.

Front 41

What is the difference between Nodejs, AJAX, and jQuery

Back 41

The one common trait between Node.js, AJAX, and jQuery is that all of them are the advanced implementation of JavaScript. However, they serve completely different purposes.

Node.js –

It is a server-side platform for developing client-server applications. For example, if we’re to build an online employee management system, then we won’t do it using client-side JS. But Node.js can certainly do it as it runs on a server similar to Apache, and Django not in a browser.

AJAX (aka Asynchronous Javascript and XML) –

It is a client-side scripting technique, primarily designed for rendering the contents of a page without refreshing it. There are a no. of large companies utilizing AJAX such as Facebook and Stack Overflow to display dynamic content.

jQuery –

It is a famous JavaScript module that complements AJAX, DOM traversal, looping, and so on. This library provides many useful functions to help in JavaScript development. However, it’s not mandatory to use it but as it also manages cross-browser compatibility, so can help you produce highly maintainable web applications.