Snake / one turn per tick

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a{margin-right:12px}.answerLine{font-size:21px;font-weight:700}.keypad{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:7px}.keypad button{min-height:43px;padding:8px 5px}textarea{overflow-wrap:anywhere}@media(max-width:720px){.docGrid{grid-template-columns:1fr}.three{grid-template-columns:1fr}.gameArea{max-width:540px}.boardSplit{gap:12px;grid-template-columns:minmax(0,1fr) 112px}}@media(max-width:400px){.boardSplit{grid-template-columns:minmax(0,1fr) 96px;gap:9px}.gameControls button{font-size:13px}.gameBoard{border-width:5px;gap:1px}.keypad{gap:5px}.scorebar{gap:16px}.scorebar strong{font-size:22px}}</style></head><body><main><header><div class="eyebrow">Original JavaScript teaching game / 10 × 10 board</div><h1>Snake / one turn per tick</h1></header>
<section class="gameArea panel gameArena" id="arena" tabindex="0" aria-label="Snake game area"><div class="scorebar"><div>Food eaten<strong id="score">0</strong></div><div>Length<strong id="length">3</strong></div><div>State<strong id="status">Paused</strong></div></div><div class="boardSplit"><div id="board" class="gameBoard" role="img" aria-label="10 by 10 Snake board"></div><div class="gameControls"><button id="resume" class="primary">Resume</button><button id="pause">Pause</button><button id="up">↑ Up</button><div class="row" style="gap:5px;grid-template-columns:1fr 1fr"><button id="left" aria-label="Turn left">←</button><button id="right" aria-label="Turn right">→</button></div><button id="down">↓ Down</button><button id="reset">Reset</button></div></div><p id="message" class="state" role="status">Paused with food directly ahead. Resume to begin.</p><p class="caption">Head ● / body ■ / food ◆. Arrow keys turn; Space pauses or resumes.</p></section>
<section class="panel below"><h2>Inspect the rules</h2><p class="muted">Use native buttons or focus the game area for keyboard controls. Moving focus outside the game area or hiding the page pauses play. Resume starts a fresh interval; no catch-up ticks. Source is included in this file.</p><p>Illustrative 150 ms ticks. Only the first valid perpendicular turn is queued per tick. A same-direction or opposite request does not consume the queue. On a non-growing step, the old tail cell is vacated before collision is checked; food keeps it occupied. Walls and other body cells end the game. A full board wins without searching randomly forever.</p><div id="trace" class="record"></div><a href="https://cs.brown.edu/courses/csci0300/2023/assign/projects/project1.html">Ordered growth and tail-vacancy reference</a></section><details class="panel below"><summary>Manual browser checks / pending parent review</summary><table><thead><tr><th>Action</th><th>Expected observation</th></tr></thead><tbody><tr><td>Resume, first tick</td><td>Food ahead is consumed; score 1, length 4.</td></tr><tr><td>Press Down then Left within one tick</td><td>Only Down applies.</td></tr><tr><td>Pause, leave controls, hide page</td><td>No movement; queued turn cleared; explicit Resume required.</td></tr><tr><td>Reset while a tick is pending</td><td>Original paused body and food return; no delayed movement.</td></tr></tbody></table><p class="muted">Also inspect focus, touch controls and overflow at 360, 720 and 1440 px. Local scripted logic checks are retained separately; these browser observations remain pending.</p></details><footer class="below muted">Local working example. Edits last only while this page is open.</footer></main><script data-app>
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const vectors={up:[-1,0],right:[0,1],down:[1,0],left:[0,-1]},opposite={up:'down',down:'up',left:'right',right:'left'};
class Snake{constructor(random=Math.random){this.random=random;this.epoch=0;this.reset()}reset(){this.epoch++;this.body=[[4,4],[4,3],[4,2]];this.direction='right';this.queued=null;this.food=[4,5];this.score=0;this.status='paused'}resume(){if(this.status==='paused')this.status='running'}pause(){if(this.status==='running')this.status='paused';this.queued=null}turn(d){if(this.status!=='running'||!vectors[d]||this.queued||d===this.direction||d===opposite[this.direction])return false;this.queued=d;return true}step(epoch=this.epoch){if(epoch!==this.epoch||this.status!=='running')return false;const d=this.queued||this.direction;this.queued=null;this.direction=d;const v=vectors[d],head=[this.body[0][0]+v[0],this.body[0][1]+v[1]],growing=this.food&&head[0]===this.food[0]&&head[1]===this.food[1];const occupied=growing?this.body:this.body.slice(0,-1);if(head.some(n=>n<0||n>=10)||occupied.some(c=>c[0]===head[0]&&c[1]===head[1])){this.status='lost';return false}this.body.unshift(head);if(growing){this.score++;const occupied=new Set(this.body.map(c=>c.join(','))),free=[];for(let r=0;r<10;r++)for(let c=0;c<10;c++)if(!occupied.has(r+','+c))free.push([r,c]);if(!free.length){this.food=null;this.status='won'}else this.food=free[Math.min(free.length-1,Math.floor(this.random()*free.length))]}else this.body.pop();return true}}
const game=new Snake();let timer=null,clock=0;for(let i=0;i<100;i++){const c=document.createElement('span');c.className='cell';c.setAttribute('aria-hidden','true');$('board').append(c)}$('board').style.gridTemplateColumns='repeat(10,1fr)';
function render(){const body=new Map(game.body.map((c,i)=>[c.join(','),i]));[...$('board').children].forEach((c,i)=>{const key=Math.floor(i/10)+','+i%10,idx=body.get(key),food=game.food&&game.food.join(',')===key;c.className='cell'+(idx===0?' head':idx!==undefined?' body':food?' food':'');c.textContent=idx===0?'●':idx!==undefined?'■':food?'◆':''});text('score',game.score);text('length',game.body.length);text('status',game.status[0].toUpperCase()+game.status.slice(1));text('message',game.status==='lost'?'Collision. Reset to play again.':game.status==='won'?'Board filled. You won.':game.status==='paused'?'Paused. Resume when ready.':'Running. First valid turn per tick.');text('trace','Head→tail: '+game.body.map(c=>'['+c+']').join(' ')+'\nCommitted: '+game.direction+'; queued: '+(game.queued||'none')+'; food: '+(game.food?'['+game.food+']':'none'));$('resume').disabled=game.status!=='paused';$('pause').disabled=game.status!=='running';['up','down','left','right'].forEach(d=>$(d).disabled=game.status!=='running');}
function stop(){clock++;if(timer!==null)clearTimeout(timer);timer=null}function schedule(){stop();if(game.status!=='running')return;const token=clock,epoch=game.epoch;timer=setTimeout(()=>{if(token!==clock||epoch!==game.epoch||game.status!=='running')return;timer=null;game.step(epoch);render();schedule()},150)}function pause(){stop();game.pause();render()}function resume(){$('arena').focus({preventScroll:true});game.resume();render();schedule()}on('resume','click',resume);on('pause','click',pause);on('reset','click',()=>{stop();game.reset();render()});Object.keys(vectors).forEach(d=>on(d,'click',()=>{game.turn(d);render()}));on('arena','keydown',e=>{const dirs={ArrowUp:'up',ArrowDown:'down',ArrowLeft:'left',ArrowRight:'right'};if(dirs[e.key]){e.preventDefault();if(!e.repeat){game.turn(dirs[e.key]);render()}}else if(e.code==='Space'&&e.target.id==='arena'){e.preventDefault();if(!e.repeat)(game.status==='running'?pause:resume)()}});on('arena','focusout',e=>{if(!$('arena').contains(e.relatedTarget))pause()});document.addEventListener('visibilitychange',()=>{if(document.hidden)pause()});window.app={Snake,game,render,resume,pause,schedule};render();
})();
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