What Happens When You Run a Node.js File?

1. Definition

When you run a Node.js file (e.g., using node app.js), Node.js executes the JavaScript code using its internal engine and starts processing tasks using the event-driven architecture.

2. Step-by-Step Execution Flow

Node.js starts and loads the file
V8 engine compiles JavaScript to machine code
Global execution context is created
Synchronous code runs line by line
Async tasks are sent to libuv
Event loop starts handling callbacks

3. Internal Components Involved

V8 Engine: Executes JavaScript
Call Stack: Handles function execution
libuv: Manages async operations
Event Loop: Executes callbacks

4. Example

console.log("Start");

setTimeout(() => {
  console.log("Async Task");
}, 0);

console.log("End");

// Output:
// Start
// End
// Async Task

5. Important Notes

Synchronous code runs first
Async tasks are handled later
Event loop manages execution order

6. Advantages

Efficient execution model
Handles async operations smoothly
Supports scalable applications