What is Event Loop?
See how the call stack, Web APIs, microtasks and the task queue decide the order your code runs in.
Event Loop Visualizer
See how the call stack, Web APIs, microtasks and the task queue decide the order your code runs in. Interactive step-by-step animation with JavaScript code, complexity and front-end use cases.
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Event Loop Visualization and Animation
See how the call stack, Web APIs, microtasks and the task queue decide the order your code runs in. Synchronous code runs on the call stack until it is empty. Promise callbacks wait in the microtask queue; timers and events wait in the task queue. When the stack is empty the event loop runs every microtask, then takes one task, and repeats. Time complexity: n/a. Space complexity: n/a. Explains why setTimeout(fn, 0) runs after promises, why long tasks freeze the page, and most async bugs.
How to use Event Loop Visualizer
- Synchronous code runs on the call stack until it is empty.
- Promise callbacks wait in the microtask queue; timers and events wait in the task queue.
- When the stack is empty the event loop runs every microtask, then takes one task, and repeats.
- Press Play, or step through with the arrow buttons and change the input to see how it reacts.
Questions
What is the time complexity of Event Loop?
Time: n/a. Space: n/a.
Where do front-end developers use Event Loop?
Explains why setTimeout(fn, 0) runs after promises, why long tasks freeze the page, and most async bugs.
Does this upload my data?
No. This converter runs in your browser for ordinary use, so the input is not sent to a backend by this tool.
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