Returns true if the cell found at (row, col) is empty and false otherwise. Empty means == null — which catches both null (the empty-cell value) and undefined. Since an out-of-bounds read returns undefined, out-of-bounds positions count as empty too. And since array input is normalized on entry — holes and explicit undefined become null — sparse arrays are welcome as quadrille sources; only zero-copy array views — raw arrays rendered by drawQuadrille — alias your memory untouched.

Guard order matters in traversals. Because out-of-bounds counts as empty, a BFS/DFS neighbor test of isEmpty(r, c) alone happily walks off the board. Lead with isValid: isValid(r, c) && isEmpty(r, c) — the pattern the built-in reach and path queries follow.

Syntax#

isEmpty(row, col)

Parameters#

Also available as the static method Quadrille.isEmpty(value), which takes a value instead of a cell position.