1. Definition

Node.js handles concurrency using a single-threaded event loop along with asynchronous, non-blocking operations. Instead of creating a new thread for each request, it efficiently manages multiple requests at the same time.

2. Key Concepts

• Single-threaded JavaScript execution
• Event Loop for handling multiple tasks
• Non-blocking I/O operations
• Thread pool (libuv) for heavy tasks

3. How it Works

• Multiple requests come to the server
• Main thread quickly registers the requests
• Time-consuming tasks are sent to background threads
• Event Loop keeps checking completed tasks
• Callback functions are executed when tasks are done

4. Example

console.log("Start");

setTimeout(() => {
  console.log("Task completed");
}, 2000);

console.log("End");

👉 Output:

Start
End
Task completed

👉 Even though the task takes 2 seconds, Node.js does not block execution.

5. Why This is Important

• Handles thousands of users efficiently
• No need to create multiple threads
• Better performance for I/O-heavy tasks
• Ideal for real-time applications

6. Advantages

• High scalability
• Efficient resource usage
• Fast response handling

7. Disadvantages

• Not suitable for CPU-heavy tasks
• Blocking code can affect entire application