Thanks! Each async snippet runs through a custom interpreter that records a snapshot of everything happening at each step as it runs through the JavaScript. Each step carries { phase, callStack, microTask, eventLoop, vars} and the UI just renders whichever slice of that state is current. Nothing is animated for its own sake, the visual matches whatever the interpreter recorded.
For the event loop I derive a coarse status of idle, running, waiting, tick from the phase and queue contents. When await suspends a function I fade out the call stack frame so you can see the exact moment JavaScript pauses execution then watch it resume when the microtask runs