Promise vs setTimeout - Which Runs First? Event Loop Mechanics
Javascript Event Loop and Queues - Vanakkam Javascript - JS Tutorial | Tamil | 2025 | Part 3
This video is made in collaboration with JS Lovers Community.
Everything covered in this video is explained in detail in the following link : https://dev.to/jslovers/mastering-asy...
Chapters:
00:00 Intro
00:50 Single-Threaded Language
01:20 Call Stack
02:28 Web APIs
07:23 JS execution Flow
07:55 Example 1 (Basic)
11:50 Example 2
19:12 Example 3 (Advanced)
27:09 Task Starvation
28:38 Key Takeaways
29:50 Conclusion
Learn how the browser event loop, task queue, microtask queue, and Web APIs work together to enable non-blocking, asynchronous JavaScript.
JavaScript is a synchronous, single-threaded language, but async operations like setTimeout, fetch, and event listeners rely on the event loop, microtasks, and macrotasks for execution.
🔹 Key Concepts:
✅ JavaScript executes synchronous code first.
✅ Asynchronous tasks use Web APIs and the event loop.
✅ Microtasks (Promises, MutationObserver) execute before Macrotasks (setTimeout, event listeners).
✅ Fetch responses (microtasks) execute before setTimeout callbacks (macrotasks).
✅ Task starvation can occur if microtasks keep running without allowing macrotasks.
By mastering these, you can write efficient & bug-free async JavaScript! 🚀
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