I thought the same, I tried it and it complained that the object doesn't support that method. I may have overlooked something, but I didn't play with it too much. My guess was that SPCascadeDropdowns hooks onto the dblclick event and somehow two clicks in a row gets interpreted as a double click. It's confusing and weird.
Note that myAddButton is the actual Add button object used with the multi LK field, not to be confused with the source list object (SelectCandidate) which relies on the user double clicking an item. So as a button, I guess it wouldn't have a dblclick method. Even stranger, part of the underlying behavior by SharePoint is to disable the Add button after clicking it, so it's like the second click() is with a disabled button..
Note that myAddButton is the actual Add button object used with the multi LK field, not to be confused with the source list object (SelectCandidate) which relies on the user double clicking an item. So as a button, I guess it wouldn't have a dblclick method. Even stranger, part of the underlying behavior by SharePoint is to disable the Add button after clicking it, so it's like the second click() is with a disabled button..