Question on registering move in logic

[medavas]

Hello, I was wondering if someone can speak to onMove in this snippet is being invoked instead of called with parenthesis. I wrote my own validation for this and not understanding how the move that is played on chessground gets passed into the validator such as () => onMove(from, to, promoteTo), I see this example is using chess.js. Let me know if I can clarify anything. Thanks for your time.

Ryan

<Chessground
  width="38vw"
  height="38vw"
  turnColor={turnColor()}
  movable={calcMovable()}
  lastMove={lastMove}
  fen={fen}
  onMove={onMove}
  style={{ margin: "auto" }}
/>

[medavas]

After some research I see it has something to do with 0x88 board representation. However when I move a piece on the board and try logging the information being passed from that move, all I get is undefined. Is there a gotcha with 0x88 where you can't log it with javascript?