JS Visualizer is a free, interactive tool that animates JavaScript execution in real time.
Paste any code, hit Run, and watch every step unfold across six synchronized panels:
• Call Stack — see functions push and pop as they execute
• Web APIs — track where setTimeout, fetch, and Promises live while waiting
• Task Queue — macrotask callbacks lined up for their turn
• Microtask Queue — Promise callbacks that always flush before the next task
• Event Loop — the orchestrator deciding what runs next
• Console — real-time output so you can verify the execution order
Features:
• 20+ built-in examples covering async/await, closures, Promises, and timer ordering
• Breakpoints — click the editor gutter to pause at any line
• Step mode — advance one action at a time
• Speed control — slow down or speed up the animation
• Shareable URLs — send your code + state to anyone
Built for developers, students, and anyone who's ever been confused by "Why does this print in this order?"
No signup. No ads. Just open it and start learning.
