JavaScript Event Loop & Asynchronous Programming

Published: 05 May 2026
on channel: freeCodeCamp.org

25,233

1.2k

Master the JavaScript Event Loop. This video uses detailed animations and diagrams to show you exactly how JavaScript manages asynchronous tasks while remaining single-threaded.

Course from ‪@FrontendDevs1991‬

❤️ Support for this channel comes from our friends at Scrimba – the coding platform that's reinvented interactive learning: https://scrimba.com/freecodecamp

⭐️ Contents ⭐️
– 00:00 Introduction to the JavaScript Event Loop
– 01:33 Components of the Browser Runtime (Engine, Stack, APIs, and Queues)
– 02:13 Understanding the Call Stack and Synchronous Execution
– 04:33 The Limitations of the Call Stack
– 06:46 Introduction to Web APIs: JavaScript's Superpowers
– 10:02 How JavaScript Handles Delays (setTimeout Example)
– 14:21 The Role of the Task Queue (Callback Queue)
– 16:34 The Event Loop: Connecting the Queue to the Stack
– 19:00 Example: Geolocation API and User Permissions
– 22:26 Example: DOM Events and Event Listeners
– 27:23 Promises, Fetch, and the Microtask Queue
– 34:54 Handling Long-Running Synchronous Tasks
– 38:35 What Goes into the Microtask Queue? (Promises, Async/Await)
– 41:05 Starvation of Functions in the Callback Queue
– 44:59 Visualizing Internals in the Browser
– 45:38 Conclusion and Final Summary

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