CellChange type

const handleChangesOnDefaults = (changes: CellChange[]) => { // evaluates as `Change<TextCell> | Change<Datecell> | ...`
  changes.forEach(change => {
    if (change.type === 'checkbox') {
      console.log(change.newCell.checked);
      console.log(change.initialCell.checked);
    }
  });
};

const handleChangesOnDefaultsAndFlagCell = (changes: CellChange<DefaultCellTypes | FlagCell>[]) => { // evaluates as `Change<TextCell> | Change<Datecell> | ... | Change<FlagCell>`
  changes.forEach(change => {
    if (change.type === 'flag') {
      // `FlagCell` specyfic fields are now available
      console.log(change.newCell.text);
      console.log(change.initialCell.text);
    }
  });
};

const handleChangesOnlyOnDateCell = (changes: CellChange<DateCell>[]) => { // evaluates as `Change<DateCell>`
  changes.forEach(change => {
    // only available type is now `date`
    if (change.type === 'date') {
      console.log(change.newCell.date);
      console.log(change.initialCell.date);
    }
  });
};

type CellChange<TCell extends Cell = DefaultCellTypes & Cell> = TCell extends Cell ? Change<TCell> : never;

interface Change<TCell extends Cell = DefaultCellTypes> {
    readonly rowId: Id;
    readonly columnId: Id;
    readonly type: TCell['type'];
    readonly initialCell: TCell;
    readonly newCell: TCell;
}