Workshop › Connect Four › Step 18 of 38

A disc on its way

What we are doing

Discs will fall instead of appearing. So play no longer changes the board: it creates falling, a disc on its way down that knows its target row. land() finishes the move: the board changes and the turn passes.

```js
let falling // the disc on its way down, or null

  falling = null

function play(col) {
  if (falling || dropRow(col) === -1) return
  const row = dropRow(col)
  falling = { col, row, who: turn, y: -CELL / 2, vy: 0 }
}

function land() {
  const { col, row, who } = falling
  board[row][col] = who
  falling = null
  turn = 3 - turn
}
```

What it means

falling is null ("nothing") when no disc is falling; if (falling || ...) refuses a move while one is.
{ col, row } is short for { col: col, row: row }. The disc starts half a cell above the canvas with speed 0.
const { col, row, who } = falling takes those three fields out into names. land puts the disc on the board.

Your turn

Under let turn write let falling; in reset, under turn = 1, write falling = null.
Change play as shown and write land under it.

Skills: Game states

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