Node js interview questions and answers mozilor technologies 2024

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IIFE (Immediately Invoked Function Expressions)

Q: What is an IIFE and why is it used?

A: An IIFE (Immediately Invoked Function Expression) is a JavaScript function that runs as soon as it is defined. It is a design pattern which is also known as a Self-Executing Anonymous Function. It is used to avoid polluting the global scope and to create a private namespace for variables.


(function() {

  // code here

})();

Single-Threaded

Q: Why is JavaScript described as single-threaded?

A: JavaScript is considered single-threaded because it has a single call stack and executes code in a single sequence. This means that JavaScript can only execute one piece of code at a time in a single thread, which can lead to blocking behavior. However, features like asynchronous callbacks and Promises allow JavaScript to perform non-blocking operations.

Promises: all vs. race

Q: What is the difference between `Promise.all` and Promise.race?

A: `Promise.all` waits for all promises to be resolved or for any to be rejected. If all the promises are resolved, it returns an array of the results. If at least one promise is rejected, it returns the reason of the first promise that was rejected.

Promise.race, on the other hand, returns the result or rejection of the first promise that resolves or rejects.

Explain Your Last Project

Q: Can you explain your last JavaScript project?

A: This answer will vary depending on the individual's experience. The respondent should describe the project's goal, the JavaScript technologies used, and the outcomes achieved.

Technical Challenge and Solution

Q: Explain a technical challenge you faced in your last project and how you solved it.

A: This answer will be subjective. The respondent should describe a specific problem, how it impacted the project, and the steps they took to resolve it, highlighting their problem-solving skills and technical proficiency.

Debugging an Error in E-commerce Application

Q: How would you debug an error in an e-commerce application?

A: Debugging an e-commerce application involves several steps:

  1. Reproduce the error to understand the conditions that trigger it.

  2. Check the console for any error messages or warnings.

  3. Use debugging tools like breakpoints to isolate the issue.

  4. Examine network requests and responses if the error is related to API calls.

  5. Review the code changes that preceded the error.

  6. Test fixes in a development or staging environment before deploying them.

Explain npm

Q: What is npm and what is its role in JavaScript development?

A: npm (Node Package Manager) is the world's largest software registry that hosts and manages the distribution of Node.js packages. Developers use npm to share and consume code, and it's a vital tool for managing project dependencies.

package.json

Q: What is `package.json` in a Node.js project?

A: `package.json` is a core file in a Node.js project. It holds metadata relevant to the project and is used for managing the project's dependencies, scripts, version, and much more.

package-lock.json

Q: What is `package-lock.json` and why is it important?

A: `package-lock.json` is automatically generated for any operations where npm modifies either the `node_modules` tree or package.json. It describes the exact tree that was generated, thereby ensuring that anyone who installs the dependencies will get the exact same version of the dependencies.

Reduce Function

Q: Explain the `reduce` function in JavaScript.

A: The `reduce` function is used to execute a reducer function on each element of the array, resulting in a single output value. It's a powerful tool for aggregating or summarizing data in an array.


const array = [1, 2, 3, 4];

const sum = array.reduce((accumulator, currentValue) => accumulator + currentValue, 0);

String Reverse

Q: How can you reverse a string in JavaScript?

A: You can reverse a string by converting it into an array, reversing the array, and then joining it back into a string.


const string = "hello";

const reversedString = string.split('').reverse().join('');

Advantage of IIFE

**Q

: What are the advantages of using an IIFE in JavaScript?**

A: IIFEs help in avoiding pollution of the global namespace, encapsulating code, and managing privacy. They also allow for the creation of new variable scopes.

CORS for Specific IP

Q: What happens if you set CORS to allow a particular IP and try to access it through Postman from a different IP?

A: CORS policies are enforced by the browser, and since Postman is not a browser, it doesn't respect CORS policies. Thus, setting CORS for a specific IP would not restrict access via Postman or other similar tools.

Middlewares

Q: What are middlewares in the context of web development?

A: Middlewares are functions that have access to the request object, the response object, and the next middleware function in the application’s request-response cycle. They can execute any code, make changes to the request and the response objects, end the request-response cycle, and call the next middleware in the stack.

Node.js and Single-Threaded

Q: Why is Node.js called single-threaded even though it can handle concurrent connections efficiently?

A: Node.js is called single-threaded because it uses a single thread for executing JavaScript code. However, under the hood, Node.js uses multiple threads through the libuv library to handle asynchronous I/O operations, which allows it to handle concurrent connections efficiently.

Event Loop

Q: What is the event loop in Node.js?

A: The event loop is a mechanism in Node.js that allows it to perform non-blocking I/O operations. Despite JavaScript being single-threaded, the event loop enables Node.js to handle multiple operations concurrently by offloading operations to the system kernel whenever possible.