웹소켓 업그레이드

<div class="n-demo"><div class="n-head"><strong>HTTP → WEBSOCKET</strong><span>LIVE TRACE</span></div><div class="n-stage"><div class="ws n-box">CLIENT</div><div class="ws-center"><div id="ws-kind">Upgrade request →</div><div id="ws-line"></div><div id="ws-message">waiting for 101</div></div><div class="ws n-box">SERVER</div></div><div class="n-foot">tap to step · auto replay</div></div>

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let step=0;function advance(){const labels=['Upgrade request →','← 101 Switching Protocols','message →','← message'];document.getElementById('ws-kind').textContent=labels[step];document.getElementById('ws-message').textContent=step<2?'HTTP handshake':'two-way channel';step=(step+1)%4}
const clickTarget=document.querySelector('.n-demo');if(clickTarget&&typeof advance==='function'){advance();const timer=setInterval(advance,1050);clickTarget.addEventListener('pointerdown',()=>{clearInterval(timer);advance()})}