Express.js Interview Questions & Answers Part- 3

Answer:

There are a few scenarios in which a Cross-Origin resource might fail in Express.js, such as:

• If it’s to a different protocol
• If it’s to a different domain
• If it’s to a different subdomain
• If it’s to a different port

Answer:

In Express.js, the response object, often referred to as res, is a crucial part of handling HTTP requests and generating responses. It is a parameter available to the callback functions of route handlers. The response object is used to send data back to the client that initiated the HTTP request. It provides methods and properties that allow you to control various aspects of the response that will be sent to the client. It is commonly used for rendering views, setting status codes, sending codes, etc.

Answer:

Here are few third-party middleware that the Express.js provides:

• Cors
• Mongoose
• Cookie-parser
• Body-parser
• Express-validator

Answer:

Express.js supports a wide range of NoSQL and RDBMS databases, such as:

• MongoDB
• PostgreSQL
• MySQL
• SQLite
• SQLite
• Oracle

Answer:

Explore the provided sanitization techniques:

• Trim() functions by removing characters from both the start and end of a string.
• Escape() alters ‘, “, <, >, &, and / to their corresponding HTML entities.
• NormalizeEmail() standardizes an email address.
• Blacklist() eradicates characters listed in the blacklist.

Answer:

In such cases, one can call the following methods:

• path– the path to which the file is written
• name– the name of the file
• type– the file’s MIME-type.
• size– the size of the file in bytes

Answer:

The Middleware, routes, and additional application logic are initialized by the server. However, the app holds the complete set of business logic that will be utilized by the server-triggered routes. This separation allows for the segregation of business logic from the application logic, contributing to the seamless operation of the system.

Answer:

In Node.js, an Event Emitter is a core module that facilitates the implementation of the observer pattern. The observer pattern is a design pattern used to establish a one-to-many dependency between objects, so that when one object (the subject) changes its state, all its dependents (observers) are notified and updated automatically.

Answer:

The following major companies use Express.js:

• Accenture
• Trustpilot
• Twitter
• Stack
• Intuit
• BlaBlaCar
• Bepro Company

Answer:

To post a query in Express.js, you’re likely referring to making an HTTP POST request to an Express.js server. Here’s a general outline of how to achieve this:

• Set Up Express Server
• Create an Express App
• Handle POST Requests
• Make POST Requests

Answer:

Following arguments are available to an Express.js route handler-function:

• Req:It is the request object
• Res:It is the response object
• Next (optional):It is a function employed to pass management to any of the above route handlers.

Answer:

Django and Express.js are both web frameworks, but they are used in different programming languages and have distinct characteristics. Here’s a brief difference between the two:

1. Programming Languages:
   • Django is a high-level web framework written in Python. It follows the “batteries-included” philosophy, offering a wide range of built-in features and tools.
   • Express.js is a minimal and flexible web framework for Node.js, written in JavaScript. It provides a simpler and more modular approach to building web applications.
2. Architecture:
   • Django follows the Model-View-Controller (MVC) architectural pattern.
   • Express.js follows the Model-View-Controller (MVC) or Model-View-Controller-Router (MVCR) architectural pattern.
3. Ease of Use:
   • Django is known for its high-level abstractions and automatic admin interface, which can make development faster, especially for projects that require common features like user authentication and admin panels.
   • Express.js is more lightweight and gives developers more control over the components they use, making it a good choice for projects where customizability is crucial.
4. Community and Ecosystem:
   • Django has a large and active community, and it offers a wide range of third-party packages and plugins that can be easily integrated into projects.
   • Express.js is part of the Node.js ecosystem, which is also known for its active community and vast selection of modules available through npm (Node Package Manager).
5. Learning Curve:
   • Django might have a steeper learning curve, especially for beginners.
   • Express.js has a relatively lower learning curve, making it more approachable for developers who are already familiar with JavaScript and Node.js.

Answer:

Express.js employs a system of request and response objects that grant access to details concerning incoming requests and outgoing responses. The request object encompasses data regarding the incoming request, encompassing the URL, method, and headers. On the other hand, the response object facilitates sending responses to the client. Developers can utilize functions like res.send(), res.json(), and res.render() to transmit responses to the client.

Answer:

The main differences between an Express.js server and a traditional server include:

• Abstraction: Express.js abstracts many complexities of server-side development, making it easier and faster to build applications.
• Routing: Express.js provides a routing system that simplifies the process of defining routes for different URLs and HTTP methods.
• Middleware: Express.js allows you to use middleware functions to handle tasks like authentication, logging, and more.
• Modularity: Express.js encourages modular code organization, making it easier to manage different parts of your application.
• Community and Ecosystem: Express.js has a large community and a wide range of third-party libraries and plugins that can further enhance your development process.

Express.js provides a higher level of abstraction and a streamlined development process compared to a traditional server.

Answer:

In Express.js, a callback function is a fundamental concept used to handle asynchronous operations. Callback functions are often used to define how the server should respond when certain events or requests occur. In the context of Express.js, a callback function is a function that is passed as an argument to another function and is executed at a later point in time, usually after a specific event or operation has completed. This is particularly useful for handling.

Answer:

In Express.js, the req.params object is used to retrieve route parameters from the URL of an incoming HTTP request. Route parameters are values that are specified within the URL route and are denoted by a colon followed by a parameter name. These parameters allow you to capture dynamic values from the URL and use them in your server-side code.

Answer:

The app.locals object in Express.js is used to store data that is available to all templates rendered within an application. This object is typically used to hold variables, functions, or data that you want to make accessible across different parts of your application, such as templates, middleware, and routes.

Answer:

Authentication can be implemented using middleware to verify user identity, such as with JSON Web Tokens (JWT) or session-based authentication. Authorization can be managed by implementing middleware that checks whether a user has the required permissions to access certain routes or resources.

Answer:

RESTful API (Representational State Transfer) is an architectural style for designing networked applications. Express.js can be used to implement RESTful APIs by defining routes that correspond to different HTTP methods (GET, POST, PUT, DELETE) and using proper status codes and data representations.

Answer:

The Router module in Express.js allows you to create modular and mountable route handlers. You can define routes within separate Router instances and then mount those routers onto your main application using app.use(). This helps organize your routes and middleware.