Grid changed (added, updated, deleted rows)

How do I know if a grid has at least one added, updated or deleted row?

You may try to use the events:

onGridReconstructed for “added”,“deleted” rows:
docs.dhtmlx.com/doku.php?id=dhtm … onstructed

onEditCell for “updated” cells:
docs.dhtmlx.com/doku.php?id=dhtm … oneditcell

Also you may use onRowAdded, onAfterRowDeleted events:
docs.dhtmlx.com/doku.php?id=dhtm … onrowadded
docs.dhtmlx.com/doku.php?id=dhtm … rowdeleted