Event loop

<div class="demo"><div class="head"><strong>EVENT LOOP</strong><span id="out">output: —</span></div><div class="scene"><div class="lane chip" id="stack">STACK<br><b>sync</b></div><span class="arrow">→</span><div class="lane chip" id="micro">MICROTASK<br><b>Promise</b></div><span class="arrow">→</span><div class="lane chip" id="task">TASK<br><b>timer</b></div></div><div class="foot"><span>sync → Promise → timer</span><span>tap to step</span></div></div>

.demo{width:min(92vw,660px);height:min(86vh,310px);border:1px solid var(--line);border-radius:14px;background:var(--surface);padding:clamp(10px,2.5vmin,20px);display:flex;flex-direction:column;gap:clamp(6px,1.7vmin,12px);box-shadow:0 10px 35px rgba(0,0,0,.07);font:500 clamp(10px,2.8vmin,15px)/1.35 ui-monospace,SFMono-Regular,Consolas,monospace}
.head,.foot{display:flex;align-items:center;justify-content:space-between;gap:8px}.head strong{color:var(--accent);font-size:1.05em}.foot{color:var(--muted);font-size:.85em;min-height:1.4em}.scene{flex:1;min-height:0;position:relative;display:flex;align-items:center;justify-content:center;gap:clamp(5px,1.5vmin,12px)}.chip{border:1px solid var(--line);background:var(--bg);border-radius:7px;padding:.4em .6em;text-align:center}.on{border-color:var(--accent)!important;background:color-mix(in srgb,var(--accent) 12%,var(--surface))!important;color:var(--accent)!important}.dim{opacity:.42}.arrow{color:var(--muted)}
.lane{width:28%;height:55%;min-height:48px;display:flex;flex-direction:column;justify-content:center;gap:.5em}.lane b{font-size:1.08em}.arrow{font-size:1.3em}

const ids=["stack","micro","task"],names=["sync","Promise","timer"];let step=0;function advance(){ids.forEach((id,i)=>document.getElementById(id).classList.toggle("on",i===step));document.getElementById("out").textContent="output: "+names.slice(0,step+1).join(" · ");step=(step+1)%3}advance();const timer=setInterval(advance,900);document.querySelector(".demo").addEventListener("pointerdown",()=>{clearInterval(timer);advance()})