MERN Stack Interview Questions | Node Js Interview Questions | | Node | MongoDB | React | Express JS

Summary

This video script is a comprehensive guide to the top 20 interview questions for Node.js, Express, MongoDB, and React. It covers essential topics like Node.js's single-threaded event loop, handling concurrency, and streams. The script also delves into MongoDB's aggregation, sharding, and replication, as well as the basics of Mongoose and the differences between synchronous and asynchronous IO. It addresses common interview questions, providing insights for both freshers and experienced candidates, and offers to create additional content based on viewer feedback.

Takeaways

• 😀 Node.js is single-threaded and uses an event loop model to handle concurrency, which allows it to manage multiple client requests efficiently.
• 🔧 When Node.js receives a request, it uses threads for operations and pushes them to the event loop, ensuring the main event loop isn't blocked.
• 📚 Streams in Node.js are essential for handling large data sets by providing data in chunks, which is useful for memory management.
• 💾 Aggregation in MongoDB groups values from multiple documents, performing operations, and returning computed results, useful for data analysis.
• 📈 Sharding in MongoDB distributes data across multiple machines, which is crucial for handling large datasets and improving performance.
• 📝 Mongoose is an Object Document Mapper (ODM) for MongoDB that facilitates schema-based modeling and offers features like typecasting and query building.
• 🔗 MongoDB does not support foreign key constraints, leaving it to the developer to manage data relationships and integrity.
• 🧵 Node.js handles side threads internally for tasks like input/output operations without exposing thread management to developers, maintaining its asynchronous nature.
• 🔁 The event loop in Node.js is a continuous process that waits for, executes, and manages tasks, operating on a last-in, first-out (LIFO) basis.
• 🌐 Node.js is built on the V8 JavaScript engine, is suitable for real-time and data-intensive applications, and operates on a non-blocking I/O model.

Q & A

How does Node.js handle concurrency being single-threaded?

Node.js uses a single-threaded event loop model architecture to handle multiple concurrent clients. It can efficiently manage more and more concurrent client requests due to its event loop, which also eliminates the need for creating multiple threads.

What is the role of the event loop in Node.js?

The event loop in Node.js is an endless loop that waits for incoming tasks, executes them, and then sleeps until it receives more tasks. It executes tasks in a Last In, First Out (LIFO) fashion and allows the use of JavaScript outside of the browser, along with callbacks and promises, making Node.js asynchronous.

What are streams in Node.js and what types of streams are there?

Streams in Node.js are a collection of data that might not be available all at once but are useful for dealing with large sets of data. Data is provided in chunks, which are consumed sequentially. There are four types of streams: readable, writable, duplex, and transform.

What is aggregation in MongoDB and how does it work?

Aggregation in MongoDB groups values from multiple documents and returns computed results. It takes multiple documents' data, runs operations defined by developers, and returns the computed results. It can perform a variety of operations on grouped data and has three ways to perform aggregation: the aggregation pipeline, the map-reduce function, and single-purpose aggregation methods.

What is sharding in MongoDB and why is it used?

Sharding in MongoDB is a method to store data across multiple machines. It is used to support deployment with large sets of data, providing redundancy and increasing data availability. Sharding protects a database from the loss of a single server by having multiple copies of data on different database servers.

What is Mongoose and how does it help in MongoDB development?

Mongoose is an Object Document Mapper (ODM) for MongoDB that allows developers to define objects and models with strongly typed schemas. It facilitates a schema-based modeling system, builds schemas for data, and offers features like typecasting, query building, and business logic.

Does MongoDB support foreign key constraints?

MongoDB does not support foreign key constraints. It does not apply any constraints to the system, so there are no cascading deletes or updates. It is up to the developers to organize data and its relationships.

How does Node.js handle child threads and why are they not exposed to developers?

Node.js is single-threaded and does not expose child thread and thread management methods to developers. However, under the hood, Node.js spawns child threads for tasks like input/output or file operations. These child threads do not block the main event loop, maintaining Node.js's asynchronous nature.

What are buffers in Node.js and what is their purpose?

Buffers in Node.js are temporary memory mainly used by streams to hold data until it's consumed. They represent a fixed length sequence of bytes and are used to handle data that cannot be fully read or written at once. Buffers are fixed allocated memory outside the V8 engine.

What is the difference between blocking I/O and non-blocking I/O in Node.js?

Blocking I/O means that the code blocks everything until the first request is finished, making the machine idle. Non-blocking I/O, or asynchronous I/O, allows other operations to continue without waiting for the first request to finish. Node.js uses non-blocking I/O, which is why it can handle a high number of requests efficiently.

What is the significance of the event loop in making Node.js asynchronous?

The event loop in Node.js is significant because it allows the system to handle asynchronous operations. It manages the execution of callbacks by processing them once the call stack is empty, enabling Node.js to perform non-blocking I/O operations and handle multiple requests concurrently.