JS Visualizer
Finally understand the JS event loop
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Supratik Das

JS Visualizer - Finally understand the JS event loop

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Watch JavaScript execute step by step. See the call stack, Web APIs, microtask & task queues, and event loop animate in real time. Finally understand why Promises fire before setTimeout and how async/await actually works. ✦ Breakpoints, step mode, speed control ✦ 20+ examples · Side-by-side comparison · Share via URL ✦ Spec-linked step explanations Free. No signup.

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Supratik Das
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Hey Product Hunt! 👋

I built JS Visualizer because I spent months explaining the JavaScript event loop to fellow developers — and words never quite worked. Diagrams helped, but they were static. What people needed was to see it move.

So I built a tool where you paste any JS snippet and watch it execute: functions entering the call stack, setTimeout callbacks waiting in Web APIs, Promises resolving through the microtask queue — all animated,
all in sync with the line of code being executed.

A few things I'm especially proud of:
→ The microtask vs. macrotask ordering is precise — it shows exactly why Promise.then() always fires before setTimeout callbacks
→ Step Explanations link to the ECMAScript spec section for each action
→ The guided tour walks first-time users through every panel
→ Everything is shareable via a single URL

It's completely free, no account needed. Just paste code / select any example and hit Run.

Would love your feedback — there's literally a Feedback button in the corner 😄 What examples or features would make this more useful for you?