Async cancellation

<div class="v"><header><b>CANCEL → CLEANUP</b><span id="state"></span></header><main><div class="steps" id="steps"></div><div class="notice" id="notice"></div></main><footer>signal, observe, clean up</footer></div>

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let n=0;const labels=["running","signal","cleanup","stopped"];function draw(){document.getElementById("steps").innerHTML=labels.map((x,i)=>"<b class=\""+(i===n?"active":i>n?"muted":"")+"\">"+x+"</b>").join("");document.getElementById("notice").textContent=n===2?"release resources before exit":n===3?"no child left running":"parent controls lifetime";document.getElementById("state").textContent=labels[n];n=(n+1)%4}draw();setInterval(draw,950)