Node.js Interview Questions(2)

系统管理员 2023-10-13 19:13 10阅读 0赞

# 1) What are the modules in Node.js? Which are the different modules used in Node.js? #

In Node.js applications, modules are like JavaScript libraries and include a set of functions. To include a module in a Node.js application, we must use the require() function with the parentheses containing the module’s name.

Node.js has several modules which are used to provide the basic functionality needed for a web application. Following is a list of some of them:  
![在这里插入图片描述][f80a0d3636e5427095872e64eed294dc.png]

# 2) What are buffers in Node.js? #

In general, a buffer is a temporary memory mainly used by the stream to hold on to some data until it is consumed. Buffers are used to represent a fixed-size chunk of memory allocated outside of the V8 JavaScript engine. It can’t be resized. It is like an array of integers, which each represents a byte of data. It is implemented by the Node. js Buffer class. Buffers also support legacy encodings like ASCII, utf-8, etc.

# 3) What is error-first callback? #

Error-first callbacks are used to pass errors and data. If something goes wrong, the programmer has to check the first argument because it is always an error argument. Additional arguments are used to pass data.

# 4) What is an asynchronous API? #

All the API’s of Node.js library are asynchronous means non-blocking. A Node.js based server never waits for an API to return data. The Node.js server moves to the next API after calling it, and a notification mechanism of Events of Node.js responds to the server for the previous API call.

# 5) How can you avoid callbacks? #

To avoid callbacks, you can use any one of the following options:

You can use modularization. It breaks callbacks into independent functions.  
You can use promises.  
You can use yield with Generators and Promises.

# 6) Does Node.js provide Debugger? #

Yes, Node.js provides a simple TCP based protocol and built-in debugging client. For debugging your JavaScript file, you can use debug argument followed by the js file name you want to debug.

Syntax:

node debug [script.js | -e "script" | <host>:<port>]

# 7) What is a control flow function? #

Control flow function is a generic piece of code that runs in between several asynchronous function calls.

# 8) How “Control Flow” controls the functions calls? #

The control flow does the following job:

*  Control the order of execution
 *  Collect data
 *  Limit concurrency
 *  Call the next step in a program

# 9) Is it possible to access DOM in Node? #

No, it is not possible to access DOM in Node.

# 10) What types of tasks can be done asynchronously using the event loop? #

*  I/O operations
 *  Heavy computation
 *  Anything requiring blocking

# 11) What is REPL in Node.js? #

REPL stands for Read Eval Print Loop. It specifies a computer environment like a window console or Unix/Linux shell where you can enter a command, and the computer responds with an output. It is very useful in writing and debugging the codes. REPL environment incorporates Node.js.

$ node  
    > 100 + 200  
    300  
    > 100 + ( 200 * 300 ) - 400  
    59700  
    >

# 12) Explain the tasks of terms used in Node REPL. #

Following are the terms used in REPL with their defined tasks:

Read: It reads user’s input; parse the input into JavaScript data-structure and stores in memory.

Eval: It takes and evaluates the data structure.

Print: It is used to print the result.

Loop: It loops the above command until user press ctrl-c twice to terminate.

# 13) Is it possible to evaluate simple expressions using Node REPL? #

Yes. You can evaluate simple expressions using Node REPL.

# 14) What is the use of the underscore variable in REPL? #

In REPL, the underscore variable is used to get the last result.

C:\Nodejs_WorkSpace>node  
    > var x = 10  
    undefined  
    > var y = 20  
    undefined  
    > x + y  
    30  
    > var sum = _  
    undefined  
    > console.log(sum)  
    30  
    undefined  
    >

# 15) Does Node.js supports cryptography? #

Yes, Node.js Crypto module supports cryptography. It provides cryptographic functionality that includes a set of wrappers for open SSL’s hash HMAC, cipher, decipher, sign and verify functions. For example:

const crypto = require('crypto');    
    const secret = 'abcdefg';    
    const hash = crypto.createHmac('sha256', secret)    
                       .update('Welcome to JavaTpoint')    
                       .digest('hex');    
    console.log(hash);

# 14) What is npm? What is the main functionality of npm? #

npm stands for Node Package Manager. Following are the two main functionalities of npm:

Online repositories for node.js packages/modules which are searchable on search.nodejs.org  
Command line utility to install packages, do version management and dependency management of Node.js packages.  
38) What tools can be used to assure a consistent style in Node.js?  
Following is a list of tools that can be used in developing code in teams, to enforce a given style guide and to catch common errors using static analysis.

JSLint  
JSHint  
ESLint  
JSCS

# 15) What is the difference between operational and programmer errors? #

Operational errors are not bugs, but create problems with the system like request timeout or hardware failure. On the other hand, programmer errors are actual bugs.

# 16) What is the difference between the global installation of dependencies and local installation of dependencies? #

Global installation of dependencies is stored in /npm directory. While local installation of dependencies stores in the local mode. Here local mode refers to the package installation in node\_modules directory lying in the folder where Node application is present.  
Globally deployed packages cannot be imported using require() in Node application directly. On the other hand, locally deployed packages are accessible via require().  
To install a Node project globally -g flag is used.

C:\Nodejs_WorkSpace>npm install express ?g

To install a Node project locally, the syntax is:

C:\Nodejs_WorkSpace>npm install express

# 17) What is the use of a buffer class in Node.js? #

The Node.js provides Buffer class to store raw data similar to an array of integers but corresponds to a raw memory allocation outside the V8 heap. It is a global class and can be accessed in an application without importing a buffer module. Buffer class is used because pure JavaScript is not compatible with binary data. So, when dealing with TCP streams or the file system, it’s necessary to handle octet streams.

# 18) What is the role of assert in Node.js? #

The Node.js Assert is a way to write tests. It provides no feedback when running your test unless one fails. The assert module provides a simple set of assertion tests that can be used to test invariants. The module is intended for internal use by Node.js, but can be used in application code via require (‘assert’). For example:

var assert = require(‘assert’);  
function add (a, b) \{  
return a + b;  
\}  
var expected = add(1,2);  
assert( expected === 3, ‘one plus two is three’);

# 19) What are the streams in Node.js? #

The Streams are the objects that facilitate you to read data from a source and write data to a destination. There are four types of streams in Node.js:

Readable: This stream is used for reading operations.  
Writable: This stream is used for write operations.  
Duplex: This stream can be used for both reading and write operations.  
Transform: It is a type of duplex stream where the output computes according to input.

# 20) What is event-driven programming in Node.js? #

In Node.js, event-driven programming means as soon as Node starts its server, it initiates its variables, declares functions and then waits for an event to occur. It is one of the reasons why Node.js is pretty fast compared to other similar technologies.  
![在这里插入图片描述][0a67d29072a6422683800662e1ea589c.png]

[f80a0d3636e5427095872e64eed294dc.png]: https://img-blog.csdnimg.cn/f80a0d3636e5427095872e64eed294dc.png
[0a67d29072a6422683800662e1ea589c.png]: https://img-blog.csdnimg.cn/0a67d29072a6422683800662e1ea589c.png