Mean Stack Interview Questions & Answers (2025)

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In TypeScript, a class is a blueprint for an object, while an interface is a contract for the shape of an object.

A class can have properties and methods, and can also include a constructor for initializing the object. Classes can also have access modifiers (such as "public" or "private") to control the visibility of its members.

on the other hand, an interface only defines the structure of an object, including its properties and methods, but does not provide any implementation. It can be used to define a contract that multiple classes can implement. Interfaces do not have access modifiers.

Additionally, a class can implement multiple interfaces, but can only inherit from one other class.

In JavaScript, a closure is a function that has access to the variables and functions defined in its outer scope, even after the outer function has returned.

Here is an example of a closure in JavaScript:

function outerFunction() {
  let outerVariable = 'I am the outer variable';

  function innerFunction() {
    console.log(outerVariable);
  }

  return innerFunction;
}

let myClosure = outerFunction();
myClosure();  // logs "I am the outer variable"

JavaScript does not have native support for modules, but you can use various tools and libraries to achieve the same functionality.

One popular way to implement modules in JavaScript is through the use of the 'module' and export keywords in the ECMAScript (ES)6 standard. You can use the 'export' keyword to make properties and methods available to other parts of your code, and the 'import' keyword to consume those exports in other files.

For example, in a file named 'math.js':

export function add(a, b) {
    return a + b;
}

export function multiply(a, b) {
    return a * b;
}

And in another file, 'main.js':

import { add, multiply } from './math';

console.log(add(1, 2)); // 3
console.log(multiply(2, 3)); // 6

Another popular way is by using module bundlers like webpack or browserify, which will bundle all the modules together in a single file that can be loaded by the browser.

You can also use a package manager like npm or yarn to manage your dependencies and to include modules from npm registry.

Note that some older browsers may not support ES6 modules natively, so you may need to use a transpiler like Babel to convert your code to a version of JavaScript that is supported by older browsers.

Some common design patterns in object-oriented JavaScript are as follows -

Constructor pattern: This pattern creates objects with a constructor function that sets the initial state and methods of the object.

Module pattern: This pattern creates a singleton object that provides a private and public interface to a set of functions and data.

Prototype pattern: This pattern creates objects that inherit properties and methods from a prototype object.

Revealing module pattern: This pattern creates a singleton object that provides a private and public interface to a set of functions and data, with the added benefit of only exposing the methods and properties you want to.

Factory pattern: This pattern creates objects without specifying the exact class of object that will be created.

Command pattern: This pattern encapsulates a request as an object, separating the request from the object that handles it.

The major differences between linear searches and binary searches are - 

Linear search: 

Linear search checks each element in the data set in sequence, starting from the first element, until it finds the element it is looking for. It is also called sequential search. It has a time complexity of O(n) where n is the number of elements in the data set. It is simple to implement and can be used with any type of data set, but it is not efficient for large data sets.

Binary search:

Binary search is used on a sorted data set and it works by dividing the data set in half and checking whether the element it is looking for is in the first half or the second half. It then continues to divide the half that contains the element in question and checks again, until it finds the element. It has a time complexity of O(log n) which is much faster than linear search for large data sets. The downside is that the data set needs to be sorted and it is only applicable for numerical or string data that can be ordered.

In summary, Linear search is simpler to implement, but less efficient for large data sets. While binary search is more efficient for large data sets, but requires the data set to be sorted and is only applicable for ordered data.

Callback is a function that is passed as an argument to another function and is executed after some event or action occurs. The function that accepts the callback is often referred to as the "parent" function, and the function that is passed in as an argument is referred to as the "callback" function.

In Node.js, callbacks are used extensively to handle asynchronous operations. For example, when reading a file or making an HTTP request, the Node.js runtime will not wait for the operation to complete before moving on to the next line of code. Instead, it will pass a callback function that will be executed when the operation is completed.

Pros of Callback in Node.js:

• They allow you to handle asynchronous operations, which makes your code non-blocking and efficient.
• They provide a clear separation of concerns, allowing you to handle the success and failure cases of an operation separately.
• They are widely used in Node.js and are supported by many built-in modules, allowing you to take advantage of pre-existing functionality.
• They are compatible with most versions of Node.js, and therefore they can run on most environments.

 Cons of Callback in Node.js:

• They can lead to callback hell, which is a situation where you have nested callbacks that are hard to read and maintain.
• They don't provide a way to cancel a callback or a way to check if a callback has been called.
• They don't support the concept of return values, and it becomes difficult to handle errors when there are multiple asynchronous operations.

Containerization is a method of packaging and deploying applications in a way that makes them easy to run and scale. It involves packaging an application and its dependencies into a container, which is a standardized unit of software that includes everything the application needs to run, including the code, runtime, system tools, libraries, and settings.

Containers are self-contained and lightweight, so they can be easily moved between different environments, such as development, staging, and production. They are also isolated from the host system and from other containers, so they do not interfere with each other or with the host system.

var express = require('express')
var app = express()

// respond with "hello world" when a GET request is made to the homepage
app.get('/', function (req, res) {
  res.send('hello world')
});

Node.js is a single-threaded but highly scalable system that utilizes JavaScript as its scripting language. It uses asynchronous, event-driven I/O instead of separate processes or threads. It is able to achieve high output via single-threaded event loop and non-blocking I/O.