Workshop › Tetris-style Blocks › Step 23 of 32

Clear full rows

What we are doing

A full row disappears and everything above falls down. Because the board is a list of rows, this is two list operations: keep the rows that still have a gap, and put new empty rows on top.

```js
function clearLines() {
  const kept = board.filter((row) => row.some((cell) => cell === 0))
  const cleared = ROWS - kept.length
  if (cleared === 0) return
  board = [...Array.from({ length: cleared }, emptyRow), ...kept]
}

  clearLines()
```

What it means

• row.some((cell) => cell === 0) asks "is there at least one empty cell in this row?".
• board.filter(...) keeps only the rows where that is true: the rows that are not full, in their old order.
• ROWS - kept.length is how many rows were full.
• [...a, ...b] spreads two lists into one: cleared new empty rows first, then the kept rows. 20 rows again.
• lock clears lines after writing the piece and before the next one appears.

Your turn

1. Write clearLines above function lock() {.
2. In lock, call clearLines() above spawn().

Skills: Arrays and objects

← Play again Points for lines →

All steps

1. The well
2. The board as rows of numbers
3. Draw one cell
4. Draw the whole board
5. The number is the color
6. A piece is a small grid
7. A list of shapes
8. All seven pieces
9. Does it fit inside the well?
10. Blocks are in the way
11. Try, then move
12. Move with the arrows
13. Turn a matrix
14. Turn with Up
15. Wall kicks
16. Falling by itself
17. A random piece at the top
18. Land and lock
19. One function starts a game
20. When the pile reaches the top
21. Game Over on screen
22. Play again
23. Clear full rows
24. Points for lines
25. The side panel
26. Levels
27. Faster every level
28. A fair bag of pieces
29. The next piece
30. Drop it
31. The ghost piece
32. Build it yourself: hold a piece