Foreign key

<div class="demo"><div class="head"><b>FOREIGN KEY</b><span>orders.customer_id</span></div><div class="stage fk"><div class="cell parent">customer 7</div><div class="wire">────→</div><div class="cell child">order 51</div></div><div class="foot"><span id="fkstatus">DELETE customer 7: blocked</span><span id="fkmark">referenced</span></div></div>

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let n=0;function tick(){document.querySelector('.parent').classList.toggle('bad',!n);document.querySelector('.child').classList.toggle('on',!!n);document.getElementById('fkstatus').textContent=n?'order 51 references 7':'DELETE customer 7: blocked';document.getElementById('fkmark').textContent=n?'valid link':'referenced';n=1-n}tick();const t=setInterval(tick,1100);document.querySelector('.demo').onclick=()=>{clearInterval(t);tick()}