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Event Loop Visualizer - Free Online JavaScript Tool | IconVault

Watch the JavaScript event loop animate: call stack, Web APIs, microtask and macrotask queues. Play, step, reset. Free in your browser.

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Event Loop Visualizer

Animate the call stack, queues and Web APIs step by step

5 of 5 free uses left

Presets

Your code

Supported: console.log("..."), setTimeout(() => {...}, ms), Promise.resolve().then(() => {...}).

5 of 5 free runs left. Stepping through a trace is always free.

Step 1 of 16
Script

console.log("start") runs immediately: synchronous code never waits for the queues.

t = 0ms

Call stack

<script>

Web APIs (timers)

No active timers

Microtask queue

Empty

Macrotask queue

Empty

Console output

> start

Simplified model: real browsers also juggle rendering, network and user-input tasks, but the ordering rules shown here (sync first, then all microtasks, then one macrotask per turn) match the real engine.

About this tool

IconVault's Event Loop Visualizer makes JavaScript's concurrency model click: paste code and watch it execute across the call stack, Web APIs, timers, the microtask queue (promises), and the macrotask queue. Animated dots carry each task through the loop while the console shows the real output order.

Use the play, step, and reset controls to slow everything down and answer the classic interview question: why does this log before that? Built for students and interview prep. Free and runs fully in your browser.

Frequently asked questions

Popular searches

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