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JS Visualizer
Finally understand the JS event loop
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.
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?
About JS Visualizer on Product Hunt
“Finally understand the JS event loop”
JS Visualizer was submitted on Product Hunt and earned 4 upvotes and 1 comments, placing #85 on the daily leaderboard. 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.
On the analytics side, JS Visualizer competes within Productivity, Education and Developer Tools — topics that collectively have 1.2M followers on Product Hunt. The dashboard above tracks how JS Visualizer performed against the three products that launched closest to it on the same day.
Who hunted JS Visualizer?
JS Visualizer was hunted by Supratik Das. A “hunter” on Product Hunt is the community member who submits a product to the platform — uploading the images, the link, and tagging the makers behind it. Hunters typically write the first comment explaining why a product is worth attention, and their followers are notified the moment they post. Around 79% of featured launches on Product Hunt are self-hunted by their makers, but a well-known hunter still acts as a signal of quality to the rest of the community. See the full all-time top hunters leaderboard to discover who is shaping the Product Hunt ecosystem.
For a complete overview of JS Visualizer including community comment highlights and product details, visit the product overview.
Supratik Das
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?