From JavaScript to Node.js: Understanding What Really Happens Behind the Scenes (Part 3)

Short summary

This tutorial explains how Node.js handles synchronous vs asynchronous file operations by tracing execution through the call stack, V8, Node APIs, C++ bindings, libuv, and the OS. Synchronous calls like readFileSync block the single JavaScript thread, while async calls like readFile delegate to libuv and free the call stack immediately. The article uses step-by-step visualizations to clarify what actually waits and what doesn't.

• •Synchronous Node.js calls block the single JS thread at the call stack level
• •Async calls delegate to libuv and OS, freeing the call stack immediately
• •Execution traced through V8, Node APIs, C++ bindings, libuv, and OS layers

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