READ TIME - 3 MINUTES
In this post, you'll learn how JavaScript's Event Loop works and how it handles asynchronous operations.
This will help you write more efficient, non-blocking code, ensuring your apps run smoothly and handle heavy workloads without freezing.
Many developers struggle with asynchronous JavaScript because they don't fully grasp how the Event Loop schedules tasks, leading to inefficient code and bugs.
The Event Loop: Backbone of Asynchronous JavaScript
JavaScript is single-threaded, meaning it can only do one task at a time. However, through the Event Loop, JavaScript handles asynchronous tasks like API calls and timers in a non-blocking way. Understanding how this loop works is essential for writing responsive apps.
How It Works: Tasks and Queues
Call Stack
The call stack is where your code runs synchronously. When a function is invoked, it's added to the stack. Once it's completed, it's removed from the stack.
Web APIs
When you call asynchronous functions (like setTimeout), they're offloaded to Web APIs. JavaScript waits for them to complete and pushes the callback onto a task queue.
Task Queue
When an asynchronous operation finishes, its callback is placed into the task queue, waiting for the Event Loop to push it into the call stack when it's empty.
The Microtask Queue: Prioritizing Microtasks
Microtasks are a special type of asynchronous task, like callbacks from Promise resolutions. These tasks are placed in the microtask queue, which is given priority over the regular task queue (macrotasks). Before any macrotask is processed, the Event Loop first checks and clears the microtask queue.
Key Takeaways
JavaScript uses a single thread to execute code.
The Event Loop allows handling async tasks without blocking the main thread.
Tasks are queued in different phases, like the microtask and macrotask queues.
Poor understanding of the Event Loop handling leads to unresponsive UIs and bottlenecks.
If you want to visualize all this, you should check out this YouTube by Lydia Hallie:
Strongly recommended!
Conclusion
Grasping the Event Loop is key to mastering asynchronous JavaScript. Understanding how and when tasks are executed allows you to optimize your code for better performance and responsiveness.
By leveraging this knowledge, you can avoid tricky bugs and write more efficient, non-blocking JavaScript.
See you next Saturday!
Keep up the great work! :)
Well documented and said. Everyone should know about the event loop. It really helps in debugging faster🫰
The LOOOOP is great!! EchoAPI has ALSO transformed my workflow! Its speed and simplicity make API testing a breeze!