Interview Questions Of Callbacks And Promises For Node Js

11 Feb, 2025

Interview Questions Of Callbacks And Promises For Node Js

Interview Questions on Callbacks and Promises for Node.js

Interview Questions Of Callbacks And Promises For Node Js

Callbacks and Promises are two popular methods for handling asynchronous operations in Node.js. Callbacks pass a function as an argument to be executed after an asynchronous operation completes, while Promises provide a more structured and readable way to handle asynchronous operations by returning an object representing the eventual completion or failure of the operation. Promises are preferred over callbacks because they are easier to read and write, and they allow for more complex control flow when dealing with multiple asynchronous operations.

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Callbacks vs. Promises

1 - What is a callback function?

A callback function is a function that is passed as an argument to another function and is executed after the other function completes.

2) What is a promise?

A promise is an object that represents the eventual completion or failure of an asynchronous operation.

3) What are the advantages of using promises over callbacks?

Promises provide a more concise and readable syntax, allow for easier error handling, and enable more expressive chaining of asynchronous operations.

Callback Based Programming

4) What is the callback pattern?

The callback pattern is a mechanism for executing code after an asynchronous operation completes, typically by passing a callback function to the operation.

5) What is callback hell?

“Callback hell” occurs when a series of nested callbacks leads to code that is difficult to understand and debug.

6) How can you avoid callback hell?

To avoid callback hell, consider refactoring code into smaller, modular functions, using utility libraries for common callback patterns, and exploring alternative approaches such as promises or async/await.

7) How do you handle errors in callback based code?

Errors in callback based code can be handled by passing an error first callback as the first argument to the asynchronous function, where the error is passed as the first argument of the callback.

Promise Based Programming

8) What is the then() method?

The then() method is a function that allows you to register a callback to be executed when the promise resolves or rejects.

9) What is the catch() method?

The catch() method is a function that allows you to register a callback to be executed when the promise rejects.

10) How do you handle errors in promise based code?

Errors in promise based code can be handled by chaining a catch() method to the promise, where the error can be handled.

11 - How do you combine multiple promises?

Multiple promises can be combined using Promise.all() or Promise.race(), depending on whether you need to wait for all or any of the promises to resolve.

12) How do you handle async/await functions?

Async/await functions are special functions that allow you to write asynchronous code in a synchronous style, using the await keyword to pause the execution until the promise resolves.

13) What is the event loop in Node.js?

The event loop in Node.js is a mechanism that allows asynchronous operations to be executed while the main program continues to run, ensuring that the program remains responsive.

14) How do callbacks and promises interact with the event loop?

Callbacks are executed when the event loop processes callbacks that have been queued after the operation completes, while promises are resolved or rejected at some point in the future, and their callbacks are executed when the event loop processes their resolution or rejection.

15) Which approach is better, callbacks or promises?

The choice between callbacks and promises depends on the specific use case and the level of complexity in the code. Promises offer several advantages over callbacks, including better readability, error handling, and chaining capabilities, but they may not always be the optimal choice for simpler asynchronous operations.

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Course Overview
This course covers the essential concepts and implementation of callbacks and promises in Node.js. It explores asynchronous programming patterns, error handling, and the differences between the two approaches. The course also delves into best practices and common pitfalls to ensure efficient and reliable code.
Course Description
This course covers the fundamental concepts and practical applications of callbacks and promises in Node.js. Learn how to handle asynchronous operations efficiently by leveraging these techniques, gaining a solid understanding of event-driven programming in Node.js.
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Functional Tools

1 - Callbacks:

Asynchronous functions that execute when a specific event occurs.

Used to handle asynchronous operations, such as I/O or network requests.

Pass a function as an argument to another function as a parameter.

The callback function gets invoked with arguments when the operation completes.

2) Promises:

Objects representing the eventual result of asynchronous operations.

Provide a more structured approach to dealing with asynchronous operations.

Create a promise object which can be in three states: pending, fulfilled, or rejected.

Resolve or reject the promise when the operation completes successfully or fails, respectively.

3) Async/Await:

Syntax that simplifies working with promises.

Mark functions as asynchronous using the ‘async’ keyword.

Use the ‘await’ operator to pause execution until the promise resolves.

Offers a more concise and synchronous like way to write asynchronous code.

4) Event Listeners:

Functions that are executed when a specific event occurs on a DOM element.

Used to respond to user interactions or other events in the browser.

Provide a way to handle asynchronous events in a structured manner.

5) HTTP Requests:

Asynchronous requests made to a server over the network.

Used to fetch or send data from/to the server.

Utilize HTTP methods like GET, POST, PUT, and DELETE.

Work with response objects to handle the received data and status codes.

6) Testing Tools:

Tools for unit testing and integration testing in Node.js.

Examples include Mocha, Chai, and Jest.

Allow developers to write tests to verify the functionality and behavior of their code.

Help ensure the reliability and correctness of the codebase.

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