JavaScript Mastermind: Count Each Symbol Once

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<html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width,initial-scale=1"><title>JavaScript Mastermind: Count Each Symbol Once</title><style>*{box-sizing:border-box}body{margin:0;color:var(--ink,#233342);background:var(--bg,#eef2f3);font:17px/1.6 system-ui,sans-serif}main{max-width:980px;margin:auto;padding:clamp(16px,4vw,38px)}h1{font:700 clamp(30px,5vw,49px)/1.12 Georgia,serif;margin:10px 0 20px;max-width:800px}h2{font-size:24px;line-height:1.3;margin:0 0 15px}h3{font-size:19px;margin:12px 0}p{margin:0 0 16px}.eyebrow{font-weight:750;letter-spacing:.08em;text-transform:uppercase;font-size:16px}header{padding:10px 0 25px;border-bottom:3px solid var(--accent,#24586d);margin-bottom:24px}.lede{font-size:20px;max-width:760px}.panel{background:var(--paper,#fff);padding:clamp(18px,3vw,28px);border:1px solid var(--line,#c6d1d8);border-radius:12px;margin:20px 0}.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:20px}.grid>*{min-width:0}.row{display:flex;gap:12px;flex-wrap:wrap;align-items:center;margin:16px 0}.stack>*{margin:12px 0}button{font:700 17px/1.4 system-ui,sans-serif;cursor:pointer;color:white;background:var(--accent,#24586d);border:2px solid var(--accent,#24586d);border-radius:7px;padding:11px 17px;max-width:100%;overflow-wrap:anywhere}button.secondary{background:transparent;color:var(--ink,#233342)}button[aria-pressed=true]{box-shadow:inset 0 0 0 3px #fff;outline:2px solid var(--ink,#233342)}button:disabled{opacity:.55;cursor:default}input,textarea,select{font:17px/1.5 system-ui,sans-serif;color:inherit;background:white;border:1px solid #778591;padding:10px 12px;border-radius:6px;max-width:100%;width:100%;min-width:0}input[type=checkbox]{width:22px;height:22px}textarea{min-height:110px;resize:vertical}label{display:block;font-weight:700;margin:12px 0 7px}button:focus-visible,input:focus-visible,textarea:focus-visible,summary:focus-visible,[tabindex]:focus-visible{outline:3px solid #aa3d70;outline-offset:4px}.result{padding:18px;border-left:5px solid var(--accent,#24586d);background:var(--soft,#e5eff2);white-space:pre-wrap;overflow-wrap:anywhere;margin:20px 0}.result:empty{display:none}.hint{font-size:16px;color:var(--muted,#435968)}table{border-collapse:collapse;width:100%;table-layout:fixed;margin:16px 0}th,td{text-align:left;vertical-align:top;overflow-wrap:anywhere;padding:12px 8px;border-bottom:1px solid var(--line,#c6d1d8)}caption{text-align:left;font-weight:750;margin:8px 0}details{padding:18px;border:1px dashed #7b8b96;margin:20px 0}summary{cursor:pointer;font-weight:750}pre{font:16px/1.6 ui-monospace,monospace;white-space:pre-wrap;overflow-wrap:anywhere;background:#162735;color:#f5f8fa;padding:18px;border-radius:8px}canvas,svg{display:block;max-width:100%;height:auto}footer{margin:28px 0;font-size:16px}.badge{font-weight:750;color:var(--accent,#24586d)}.metric{font:700 38px/1.3 Georgia,serif}.board{display:grid;gap:5px;max-width:440px;margin:20px auto}.board button{padding:7px;min-height:45px}.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%)}@media(max-width:560px){.grid{grid-template-columns:1fr}main{padding:16px}th,td{padding:10px 5px}.row button{flex-grow:1}.metric{font-size:32px}}
:root{--bg:#142832;--paper:#203a46;--ink:#f1f6f6;--accent:#316f83;--soft:#164454;--muted:#d0e0e5}.slots{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:12px}.slots input{font-size:26px;text-align:center;color:#183541}.symbolbank{font-size:18px}</style></head><body><main><header><p class="eyebrow">Code-breaker lab · A–F symbols</p><h1>JavaScript Mastermind: Count Each Symbol Once</h1><p class="lede">Consume exact positions before comparing the remaining symbol counts.</p><p class="hint">Original four-slot developer practice with inspectable fixed key AABC, eight valid attempts. No secure-secret or commercial scoring claim.</p></header><section class="panel"><h2>Four symbols. Eight valid attempts.</h2><p class="symbolbank">A Triangle · B Square · C Circle · D Diamond · E Star · F Hexagon</p><div class="slots"><div><label for="g1">Slot 1</label><input id="g1" maxlength="1" autocomplete="off"></div><div><label for="g2">Slot 2</label><input id="g2" maxlength="1" autocomplete="off"></div><div><label for="g3">Slot 3</label><input id="g3" maxlength="1" autocomplete="off"></div><div><label for="g4">Slot 4</label><input id="g4" maxlength="1" autocomplete="off"></div></div><div class="row"><button id="check" type="button">Check guess</button><button id="reset" type="button">Reset</button></div><p id="status" class="result" role="status">Playing · Attempts: 0 of 8.</p><p id="result" role="status"></p><h2>Guess history</h2><pre id="history"></pre><details id="developer"><summary>Developer example key</summary><p>AABC. This fixed key also exists in source; it is not protected.</p><p>AAAA → Exact 2, Misplaced 0. ADAA → 1,1. BCAA → 0,4.</p></details></section><footer>Compare AAAA, ADAA and BCAA to see how repeated symbols affect the two totals.</footer></main><script>
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