Match-3 JavaScript: Clear the Union, Then Apply Gravity

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<body class="game"><main><header><div class="eyebrow">Original interactive state lab</div><h1>Match-3 JavaScript: Clear the Union, Then Apply Gravity</h1><p>Two matching lines share one cell. Counting both lines separately awards six when only five cells disappear. <mark>Clear a set of coordinates once</mark>, then let survivors fall.</p></header>
<p>Finite 4×4 teaching board. No refill; each cleared coordinate earns one point.</p><nav><button type="button" id="cross">Cross fixture</button><button type="button" id="resolve">Resolve fixture matches</button><button type="button" id="reset">Reset</button></nav><div id="board" class="board four"></div><p id="result" class="result" role="status"></p><div id="ledger" class="ledger"></div>
<footer>This finite board has no refill. Reset restores all sixteen starting symbols.</footer></main><script>
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(function(){let board=[],score=0,moves=0,selected=null,phase='Ready';const seed='AABCBCABCBACABCA'.split('');function matches(b){const setOf=new Set();for(let r=0;r<4;r++)for(let c=0;c<4;c++)for(const[dr,dc]of[[1,0],[0,1]]){const v=b[r*4+c];if(!v)continue;let line=[],rr=r,cc=c;while(rr<4&&cc<4&&b[rr*4+cc]===v){line.push(rr*4+cc);rr+=dr;cc+=dc;}if(line.length>=3)line.forEach(i=>setOf.add(i));}return setOf;}function available(){for(let i=0;i<16;i++)if(board[i])for(const j of[i%4<3?i+1:-1,i<12?i+4:-1]){if(j<0||!board[j])continue;const b=board.slice();[b[i],b[j]]=[b[j],b[i]];if(matches(b).size)return true;}return false;}function render(message='',focusIndex=null){q('board').innerHTML=board.map((v,i)=>`<button type="button" id="cell${i}" class="cell ${selected===i?'chosen':''}" aria-pressed="${selected===i}" aria-label="Row ${Math.floor(i/4)} column ${i%4}: ${v||'empty'}">${v||'·'}</button>`).join('');board.forEach((_,i)=>on('cell'+i,()=>choose(i)));set('result',`${phase}; score ${score}; moves ${moves}. ${message}`);if(focusIndex!==null)q('cell'+focusIndex).focus();}function resolve(focusIndex=null){const cleared=[];let setOf=matches(board);while(setOf.size){cleared.push([...setOf].map(i=>'('+Math.floor(i/4)+','+i%4+')').join(' '));score+=setOf.size;for(const i of setOf)board[i]=null;for(let c=0;c<4;c++){const values=[0,1,2,3].map(r=>board[r*4+c]).filter(Boolean);while(values.length<4)values.unshift(null);values.forEach((v,r)=>board[r*4+c]=v);}setOf=matches(board);}phase=available()?'Ready':'NoMoves';set('ledger','Clear phases: '+(cleared.join(' / ')||'none')+'. Rows: '+Array.from({length:4},(_,r)=>board.slice(r*4,r*4+4).map(v=>v||'_').join('')).join(' / '));render('',focusIndex);}function choose(i){if(phase!=='Ready')return;if(!board[i])return render('Empty cells cannot be swapped.',i);if(selected===null){selected=i;return render('Choose an adjacent destination.',i);}const a=selected;selected=null;if(Math.abs(Math.floor(a/4)-Math.floor(i/4))+Math.abs(a%4-i%4)!==1)return render('Nonadjacent: unchanged.',i);const next=board.slice();[next[a],next[i]]=[next[i],next[a]];if(!matches(next).size)return render('No resulting match: unchanged.',i);board=next;moves++;phase='Resolving';resolve(i);}on('resolve',()=>{if(phase==='Fixture')resolve();});on('cross',()=>{board='BCDBCDABC AAADBAC'.replace(/ /g,'').split('');board=Array(16).fill(null);for(const i of[9,10,11,6,14])board[i]='A';score=0;moves=0;selected=null;phase='Fixture';set('ledger','Cross has five A coordinates; no refill.');render();});on('reset',()=>{board=seed.slice();score=0;moves=0;selected=null;phase='Ready';set('ledger','No swap yet.');render();});board=seed.slice();render();})();})();
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