Node.js Runtime Visualizer
An interactive, animated walkthrough of how JavaScript executes inside Node.js: call stack, event loop phases, microtask and macrotask queues, Node APIs, and the libuv thread pool.
The visualizer steps through a carefully crafted example that touches every async pattern in Node: synchronous calls, process.nextTick, Promises, setTimeout, setImmediate, and I/O. You can play, pause, step forward and back, and change playback speed while watching functions get pushed and popped from the call stack and callbacks move between queues.
Rather than executing real JavaScript, it is built on a deterministic simulation engine that generates a timeline of execution steps. That design gives precise control over ordering and timing, which makes it possible to show subtle behaviour like nextTick running before Promise callbacks and the event loop moving through its timers, poll and check phases.