2048 · qwen3.8-max-0902

Let's build the game. Write the full 2048 implementation to index.html, then test it in the browser.

Main design: a 4x4 grid, tiles are absolutely positioned with transitions on transform. Track a board array of tile objects (id, value, row, col, merged flag). Move logic: for each row/column in the direction of movement, traverse cells, merge equal adjacent tiles only once. Animation: move the tile element to the new position, mark merged tiles to be removed after the transition, spawn new tiles with a pop animation. Input lock during animation (or, instead of locking, use a queue — simpler: a ~120ms lock, but "prevent rapid inputs from corrupting state" — locking with an animation flag is enough; but also make sure state updates happen synchronously and animations are purely visual).

Approach: keep a board as an array of tile objects {id, value, r, c}. On move: synchronously compute the new state (positions, merges, score, spawn), then update the DOM and let CSS transitions animate. Set the animating flag briefly to ignore input, or better, allow input but keep DOM updates idempotent. Simplest and most robust: a ~150ms input lock after a move.

Let's write it.

Move algorithm:
For direction left: process each row, get non-null tiles in left-to-right order. Output: iterate, if the next tile has the same value and the previous output tile is not yet merged → merge: output tile value *2, score += merged value, the second tile moves to the same cell then gets removed.

Represent cells as a grid of tile references. Build the resulting grid.

DOM: container .board, grid background cells, tile layer. Tiles are positioned by transform translate based on r,c.

Win message at 2048 (once), with "Keep going" and "New Game" buttons. Game-over overlay when no moves possible.

Keyboard: arrow keys + WASD, preventDefault.

Let's write the code.

There's a weird leftover line: `if (!(mergedTiles.includes(...) === false && false) && grid[r0][c0] === tile)` — that's messy. Let's simplify: after the while loop, if the tile is still at grid[r0][c0] (hasn't been merged), slide it if necessary. The check `grid[r0][c0] === tile` is sufficient. That's because if it was merged, we set grid[r0][c0]=null. Let's clean this up.

Wait a sec—there's a subtle bug in the merge logic. When a tile merges into the `next` tile at (r,c), I set `grid[r0][c0]=null`, but that next tile might have already been processed (since we process in order from the closest to the edge, next has already been processed, and next.mergedFrom guards against a second merge). But there's another problem: when a tile slides without merging, if there's a merged tile at grid[r][c]... actually, the while loop stops when next exists and can't merge—meaning the tile only slides into empty cells, and grid[r][c] is empty. OK.

One issue: the merge case—`tile.r/tile.c` should be set to the merge target position for the animation of the deleted element. I execute `positionTile(t.el, t.r, t.c)` on the deleted tile, but tile.r/c is still r0,c0, so it doesn't animate to the merge position. Fix: set tile.r = r; tile.c = c before pushing to removedEls. Also, `r` inside the merge branch is set to nr,nc—so set tile.r=r; tile.c=c.

Also, styleTile gets re-executed on merged tiles — since grid[r][c] = next and the value has been doubled, the "re-render value" loop applies styles with the new value. Good. But z-index: the removed tile animates on top of the merged tile at the same z-index — no problem.

Another issue: merged tiles get restyled during the slide phase (before the animation ends) — does the value change immediately while the incoming tile is still moving? Since we're calling styleTile right after computing the move, the merged tile will instantly display the new value during the slide. It's a bit of a visual issue but acceptable; the actual typical behavior is to update after the transition. Could also delay the style update for merged tiles by 130ms. Improvement idea: inside the render loop, if the tile is included in mergedTiles, delay the style. More simply: for merged ones, set the style with setTimeout.

Edit the render loop like this:

for tiles in grid: positionTile always; if mergedTiles.includes(t) then delay styleTile with setTimeout(t=>..., ANIM_MS). But ANIM_MS is defined later. Anyway, let's restructure using a local const.

Wait — issue: merged tiles are displayed at their old value during the slide, and the deleted tile slides on top of it. That's fine (classic behavior). But the `next` tile element's style gets updated after ANIM_MS. Good.

Another issue: after merging, the merged tile `next` might need to move to a different position (no wait, next stays in its own cell, only the value changes). positionTile is called with t.r/t.c, but this doesn't change. Good.

Also about the z-index of merged tiles: the deleted tile might slide under/over next's element; the pop animation of merged tiles uses the internal scale. OK.

Next, test in the browser. Also want to test the move logic directly — expose grid for debugging? Can evaluate in the console. The IIFE hides state; but can inspect the DOM. For logic verification ([2,2,2,2] → [4,4,0,0]), could extract the algorithm, or test via DOM manipulation: hard. Alternative: temporarily expose state on window for testing? Could add a debug hook like `window.__game = {...}` — no harm in leaving it in. Let's add a small debug API.

Hmm, setGrid bypasses gameOver/animating. The test's move() checks the gameOver flag, but that's not exposed. For testing purposes it's fine — the flag is false after newGame. But wait: even after running setGrid with a custom board, moves will work.

One problem with setGrid: it doesn't reset gameOver. For now that's within acceptable range.

Let's test it in the browser.

The board renders with 2 tiles. The board's appearance is slightly off (the board's height looks vertically elongated? Actually the board is 460x460 but in the screenshot the cells look rectangular — cell width vs height: board padding is 10, cells use calc((100%-30px)/4) for both. In the screenshot the cells look wider than they are tall? Board area is about 460x460, but in the image the board is displayed from y=130 to y=590, which is 460. Cells look like about 105x105? Actually row 1: y 137-245 (about 108), columns x 375-483 (about 108). Looks square. No problem — the visual issue is that the tile at (0,1) is at x~520? Tile is at column 1: x 524-566? Hmm, tile "2" is at (545,193) — column 1, row 0. And the second one is at (657,307): column 2, row 1. Positions match the grid.

But the board looks vertically elongated: from 130 to 590 = 460. OK, square. Cells look fine.

Next, test the logic with the debug hook: set [2,2,2,2] and move left → expect [4,4,0,0] plus a spawned tile; score +8. Then [2,2,4,0] left → [4,4,0,0] score +4... wait, merging 2+2 gives 4 → score +4. Example: moving [2,2,4,0] left gives [4,4,0,0]: yes, the first two merge into 4, and 4 slides. Score +4.

Test with evaluate? The browser tool doesn't have evaluate. Actions: inspect, screenshot, click, drag, key, type, scroll. Hmm, no JS eval. "inspect" might return DOM/console. To run JS... can I use key input? No, impossible.

Alternative: verify logic via headless node? Run node with a small harness that extracts the script and simulates? The script uses DOM. Easier approach: write a simple node test that reimplements it? That wouldn't count as verifying the app.

Maybe browser's "inspect" allows evaluating expressions? Let me check the tool description: "Run index.html, inspect DOM/console, interact, view screenshots or motion frames." Actions are limited. Perhaps inspect returns DOM state. I can play moves with the key action and inspect the DOM text to verify tiles and score.

Plan:
1. Use __game? Can't call it without eval.

So test by playing: press arrow keys, inspect DOM after each move (DOM text lists tile values in order?). The DOM text in the reload output was "2048\nSCORE\n0\nBEST\n0\nNew Game\nhint\n2\n2" — tiles appear as values. But position isn't clear from the text. Screenshot shows positions.

To verify the merge example [2,2,2,2]→[4,4,0,0], I need a controlled board. Can't set it without eval... unless the browser tool has some eval capability. Let me try action "inspect" and see what comes back.

Interesting — the second screenshot shows the tiles displayed larger (did the pop/appear animation scale complete? Actually, the first screenshot was mid-animation with the tiles small). The tiles look big relative to the cells — tile at (0,1): cell area x 495-595, tile is 495-595? Covers the entire cell. Hmm, but in the first screenshot the tiles looked smaller (44px). That was mid-`appear` animation (scale). Now they're full size. But wait, the tiles look bigger than the cells? Cell (0,1): x is from 490 to 595? Tile is 495-595 ≈ 100px, cell width ≈ 105. No problem.

Hmm, but the tile font: 44px inside a 100px cell, OK.

Now: no JS eval in the browser tool. To verify merge logic precisely, I can run the same algorithm in node. Better approach: extract the script from index.html and run it in node with a minimal DOM shim? Heavy. Alternative: reproduce the move function in node and test — but that tests the copy, not the app.

Better approach: use the browser to play actual moves and verify with screenshots:
- Press ArrowLeft: tiles slide left; a new tile appears.
- Keep pressing until a merge is observed; check that the score increments by the merged value.

The starting tiles are 2 at (0,1) and 2 at (1,2). Press ArrowLeft: both slide to column 0: (0,0) and (1,0). Not adjacent in the same row, so no merge. Then ArrowUp: (1,0) moves up and merges with (0,0) → 4 at (0,0), score +4. Then a tile spawns.

This verifies slide + merge + score. Then test New Game: 2 tiles, score 0.

Also verify the [2,2,2,2] case: hard to arrange naturally. But I can trust the algorithm; still, maybe I can verify with a node-based unit test of the extracted logic. Extract the move logic and run it in node? The script is an IIFE using the DOM. I could write a small node harness that stubs document/window minimally. That's feasible: the script uses document.getElementById, createElement, addEventListener, querySelectorAll, classList, style, dataset, appendChild, firstElementChild, innerHTML setter, offsetWidth. Stubbing all of these is medium effort but doable. Given the 15-minute budget, about 10 minutes remain. Simpler: copy the move algorithm into a node test file and test the pure logic — risk of divergence, but the algorithm code is identical text; can extract via sed from between markers. Hmm.

Actually, the simplest and most robust check: the DOM stub approach is overkill. The browser play test covers slide/merge/score/spawn/new game. The [2,2,2,2]→[4,4,0,0] rule: can it occur naturally? Need a row of 2,2,2,2. Unlikely early on.

Alternative: temporarily add a URL hash debug feature? Already added __game hook but can't call it without eval. Hmm — maybe the browser tool's "type" can input into a console? No, impossible.

Wait: maybe I can use the key tool with text? No, impossible.

OK, compromise: extract the <script> contents and run in node with a jsdom-like stub. Let me quickly write a minimal DOM stub:

- document.createElement returns an element object: {className, style:{}, dataset:{}, children:[], appendChild, remove, classList:{add,remove,toggle,contains}, addEventListener, set innerHTML, textContent, firstElementChild getter, offsetWidth:0, querySelectorAll:()=>[] }
- document.getElementById returns a stub element per id.
- document.addEventListener is a noop.
- window = global.

The script uses: tileLayer.innerHTML=''; tileLayer.appendChild; el.classList; el.style.transform etc.; el.firstElementChild (the inner div created then appended, so firstElementChild = children[0]); void offsetWidth; board.focus(); document.querySelectorAll? tileLayer.querySelectorAll('.tile') — stub returns children filtered by class.

classList needs add/remove/toggle/contains backed by a Set.

styleTile sets inner.style.background etc. and inner.textContent.

positionTile sets el.style.transform.

document.createElement('div') etc.

document.addEventListener('keydown') — capture the handler so node tests can dispatch moves by calling __game.move directly.

Then tests:
1. __game.setGrid([[2,2,2,2],[0,0,0,0],[0,0,0,0],[0,0,0,0]]); move('left'); after timeout (130ms) check grid row 0 = [4,4,x,?]. Spawn adds one tile somewhere in an empty cell. Expect [4,4,0,2or4] etc. Score 8.
2. setGrid([[2,2,4,0],...]) move left → row 0 [4,4,0,spawn?]. Spawn in an empty cell of row 0 or elsewhere. Score +4.
3. No change: setGrid with a state where left move does nothing? E.g. [[2,4,8,16],...] move left → no change, no spawn, score same.
4. Game over detection: fill the board with no moves → move → gameOver overlay. Can check overlay class.
5. Win: setGrid [[1024,1024,0,0],...] move left → win overlay shows.

setTimeout is used — node has it; wait about 200ms.

This is a solid verification. Let me write the stub.

Element stub details:

function makeEl(tag){ 
 const el = {
  tag, children: [], style: {}, dataset: {},
  className: '',
  _classes: new Set(),
  appendChild(c){ this.children.push(c); c.parentNode=this; return c; },
  remove(){ if(this.parentNode){ const i=this.parentNode.children.indexOf(this); if(i>=0)this.parentNode.children.splice(i,1);} },
  get firstElementChild(){ return this.children[0] || null; },
  get classList(){ const s=this._classes; return { add:(...a)=>a.forEach(x=>s.add(x)), remove:(...a)=>a.forEach(x=>s.delete(x)), toggle:(x,f)=>{ if(f===undefined){ s.has(x)?s.delete(x):s.add(x);} else if(f) s.add(x); else s.delete(x); }, contains:x=>s.has(x) }; },
  querySelectorAll(sel){ // only '.tile'
    return this.children.filter(c=>c._classes.has(sel.slice(1)));
  },
  addEventListener(){}, 
  focus(){},
  set innerHTML(v){ this.children=[]; }, get innerHTML(){ return ''; },
  set textContent(v){ this._text=v; }, get textContent(){ return this._text||''; },
  offsetWidth: 0,
 };
 return el;
}

Note: classList as a getter returning a new object each time is fine.

className assignment: the script sets el.className='tile' — should sync with _classes. Use a defineProperty setter: set className(v){ this._classes = new Set(v.split(/\s+/).filter(Boolean)); }.

document stub:
const ids = {};
document = {
  createElement: makeEl,
  getElementById: id => ids[id] || (ids[id]=makeEl('div')),
  addEventListener: (t,f)=>{ listeners[t]=f; },
};
window = globalThis; global.window = globalThis.

The script references `document`, `window.__game = ...`. In node, define global.document, global.window.

Extract the script: sed -n '/<script>/,/<\/script>/p' index.html | sed '1d;$d' > /tmp/game.js, then require it in the test file? It's an IIFE; run via eval or require. Use `require('/tmp/game.js')` after setting globals. Then global.__game is set (window.__game = ... and window===globalThis).

Tests with async waits.

Also keydown handler: capture the listener to simulate arrow keys: listeners['keydown']({key:'ArrowLeft', preventDefault(){}}).

Let me write it.

Wait, is the script tag on its own line as `<script>`? In my file, yes, `<script>` is on its own line. 300 lines were extracted. Next, I'll write the node harness.

Note: In the game-over test using a dead board, move() returns early because moved=false, so the overlay isn't shown — but the requirement is: "Game Over only when no valid moves remain." A dead board means no valid moves exist... but how does the overlay get shown? In my implementation, gameOver is only checked after a successful move. If the board is dead, the last move that filled the board triggers the check. That's the correct behavior: after a move that changes the board and spawns, if !canMove() → game over. In the dead-board test, the move doesn't change anything → correctly no overlay (the game should already have been over before that). But wait: if the board becomes dead after a spawn, my code checks !canMove() inside the timeout → shows the overlay. Good.

Test: "Dead board: move ignored, no overlay" — since moved=false, move() returns early. Good, the overlay stays hidden. But realistically, the game-over overlay should already have been shown at the point the board became dead. No problem.

Let's also verify that game-over triggers: set the grid so that one move merges and the spawn fills the last cell making it dead... complicated. Simpler: set the grid to a state with 3 empty cells? Hmm: after the move, spawn fills one empty cell. For the board to be dead after spawn, there must be exactly one empty cell before spawn, and the spawn must create a dead board. Example: a board with 15 tiles and one empty cell, where the move merges two tiles (freeing... no, the merge frees one cell and the moving tile's cell... net: merge reduces tile count by 1 → one more empty cell; then spawn fills one → still one empty cell → canMove is true (empty cell exists). Therefore game over can only occur when the board is completely full with no merges after spawn: the board must be full after spawn → before spawn, 15 tiles and one empty cell; after the move, tile count must be 15 → the move must not merge (merge reduces count). But a move without a merge on a 15-tile board... slides tiles; count stays at 15; spawn → 16 full. Then if there are no adjacent equal tiles → dead. Example:

Board:
Row 0: 2 4 2 4
Row 1: 4 2 4 2
Row 2: 2 4 2 4
Row 3: 4 2 4 _
Move left? Row 3: [4,2,4,0] → slides to [4,2,4,_] no change... other rows can't move (full, alternating). Row 3 left: tiles are already packed left; no change. Move right: row 3 [4,2,4,0] → [_,4,2,4] changed! Then spawn fills (3,0). If spawn is 2: row 3 = [2,4,2,4]; check adjacency: (3,0)=2 vs (2,0)=2 → merge possible → not dead. If spawn is 4: [4,4,2,4] → horizontal merge possible. Hmm.

Design a dead end: after the right move and spawn, the board must have no equal adjacencies. The spawn value is random 2/4 — can't control. Pick a pattern where both 2 and 4 at the spawn cell result in a dead board: the spawn cell's neighbors must differ from both 2 and 4 → neighbors must be 8 or higher.

Board (15 tiles, empty at (3,3)):
Row 0: 2 4 2 4
Row 1: 4 8 4 8
Row 2: 2 4 2 4 … wait, vertical adjacency: (0,0)=2 vs (1,0)=4 ok; (1,0)=4 vs (2,0)=2 ok; (2,0)=2 vs (3,0)=? Row 3: 8 16 8 _ → (2,0)=2 vs 8 ok; (3,0)=8 vs (3,1)=16 ok.
Row 2: 2 4 2 4: (2,1)=4 vs (1,1)=8 ok, vs (3,1)=16 ok; (2,2)=2 vs (1,2)=4 ok vs (3,2)=8 ok; (2,3)=4 vs (1,3)=8 ok vs (3,3)= empty.
Row 0: 2 4 2 4 horizontal alternating ok. Row 1: 4 8 4 8 ok. Row 2: 2 4 2 4 ok. Row 3: 8 16 8 _ ok.
Move right: rows 0-2 are full and can't slide? Full row with no merges → no change. Row 3 [8,16,8,0] → right: [0,8,16,8] changed. Spawn at (3,0): value 2 or 4; neighbors (2,0)=2, (3,1)=16. If spawn is 2 → equals (2,0)=2 → merge possible → not dead. Damn.

Make (2,0)=8? Then column 0: (0,0)=2, (1,0)=4, (2,0)=8, (3,0)=8? No, (3,0)=8 equals (2,0)=8 → already mergeable. Column 0: 2,4,16,8; row 3: 8? (3,0)=8 vs (2,0)=16 ok. Then row 2: 16 4 2 4? (2,0)=16 vs (1,0)=4 ok vs (3,0)=8 ok; (2,1)=4 vs (2,0)=16 ok…

Board:
Row 0: 2 4 2 4
Row 1: 4 8 4 8
Row 2: 16 4 2 4 → check (2,1)=4 vs (1,1)=8 ok vs (3,1)=16 ok; (2,2)=2 vs (1,2)=4 ok vs (3,2)=8 ok; (2,3)=4 vs (1,3)=8 ok.
Row 3: 8 16 8 _ → (3,0)=8 vs (2,0)=16 ok.
Spawn cell (3,0) after right move: neighbors (2,0)=16, (3,1)=16… wait, after right move row 3 = [_,8,16,8], spawn at (3,0): neighbors (2,0)=16 and (3,1)=8. Spawn 2: no match (16,8). Spawn 4: no match. Dead! Also check the whole board after move: row 3 [2or4,8,16,8] horizontal ok; vertical (3,1)=8 vs (2,1)=4 ok; (3,2)=16 vs (2,2)=2 ok; (3,3)=8 vs (2,3)=4 ok. And rows 0-2 unchanged and dead. So after the right move + spawn → game over overlay.

Add this test. Also, the earlier "dead board" test with a full alternating board: move up: column 0 [2,4,8,16] no merge, full → no change. Good.

Let's add the game-over trigger test.

Wait: about the game-over test — but before that, the immediately preceding test left the overlay hidden. After setGrid (which doesn't touch the overlay), move right → after timeout: spawn, then check !canMove → gameOver → showOverlay('Game Over'). But note: `won` is false. OK.

However, one point: in the earlier "victory overlay" test, keepPlaying=true was set, and then g.newGame() resets it. The subsequent setGrid test is fine.

Also, the "dead board: move ignored" test comes before the game-over trigger test; the order in the file: victory test, then newGame, then unchanged-move test, then dead-board test, then (new) game-over trigger, then new-game reset. In the game-over trigger test, the overlay from the victory was already hidden by newGame. Good.

Run the test.

All logic tests pass. Includes the required examples ([2,2,2,2]→[4,4,0,0], [2,2,4,0]→[4,4,0,0]), spawn rules, win/lose overlays, new game, and resistance to fast input.

Next, browser gameplay check: play a few moves with actual arrow keys, verify slide/spawn/score via screenshots, then New Game. The current page state has the initial 2 tiles. Press ArrowLeft → both tiles slide to the left column (row 0 col 1 → col 0; row 1 col 2 → col 0). Then ArrowUp → merge into 4, score 4. Screenshot. Then click New Game → 2 tiles, score 0.

Note: the key action sends keys to the page. The board has tabindex and focus, but the keydown listener is on document, so no problem.

The screenshot was taken at frame +0ms, i.e., right after the key press, so the tiles are still in their old positions (or mid-animation). The DOM still shows two tiles. Need to wait a bit and then take a screenshot. The browser tool's "motion" action can capture frames over time. Let me press ArrowUp and then use motion/screenshot to check the state after the animation. Actually, the screenshot right after the key shows the pre-move position? The tiles are at (0,1) and (1,2) — same as before the key. The transition is 120ms, and the screenshot is at +0ms.

I'll go with pressing ArrowUp and then taking a screenshot (a separate call, which will naturally introduce a delay).

After ArrowLeft: the tiles moved to (0,0) and (1,0), and a new tile spawned at (0,2). The DOM shows three 2s. The screenshot is mid-animation of ArrowUp (the tiles at (0,0) and (1,0) are sliding upward; the two tiles in column 0 visually overlap). Good — the slide is working, and the spawn is working too.

Next, wait and take a screenshot: expect the merge → a 4 at (0,0), score 4, plus a new spawned tile.