How to get an array of selected row numbers, agnostic of whether the selection is one row, multiple rows, or multiple non-contiguous rows?

I just need to know which rows are in a user's selection when the function is run. They might select one cell, they might drag a selection across multiple cells, or they might ctrl+click multiple cells that aren't next to each other.

But whoever designed Google Apps Script seems to have decided that we're not going to have a consistent way of doing that.

getActiveRangeList()
> Return
> RangeList — The list of active ranges.

>If there is a single range selected, this behaves as a getActiveRange() call.

getActiveRange()
> Return
> Range — The active range.

Range objects have
> getRow() — Returns an integer.
> getLastRow() — Returns an integer.
> getNumRows() — Returns an integer.

RangeList objects have
> getRanges() — Returns an array containing each individual range.

I've spent hours reading dozens of articles, essays, and Stack Overflow questions about ranges, and apparently not a single one of them has figured out how to do this simple thing.

The documentation was wrong.

getActiveRangeList() does not "behave like getActiveRange()" if there is only one range.

getActiveRangeList().getRanges() returns an array containing all ranges. If there's only one, then the array has only one range in it.

getActiveRange().getRanges() crashes with an error because getRanges() doesn't exist in this case.

Therefore, we can just use getActiveRangeList() to cover all possible scenarios.

function rowChecker()
{
  var active = SpreadsheetApp.getActiveRangeList().getRanges();
  for(var n = 0; n < active.length; n++)
  {
    Logger.log(active[n].getRow());
    Logger.log(active[n].getLastRow());
  }
}

//3
//3

//1
//3

//1
//1
//3
//4

//1
//1
//2
//3
//4
//4

The order the ranges are found seems to depend on the order they were created. For example: If I create that last image starting with the bottom box, then the top box, then the middle two, the output is:

//4
//4
//1
//1
//2
//3

To get our final array of rows that have a selection in them, we can just modify the code above.

function rowChecker()
{
  var rows = [];
  var active = SpreadsheetApp.getActiveRangeList().getRanges();
  for(var n = 0; n < active.length; n++)
  {
    for(var r = active[n].getRow(); r <= active[n].getLastRow(); r++)
    {
      if(!rows.includes(r))
      {
        rows.push(r);
      }
    }
  }
  Logger.log(rows);
}

//1
//3
//4

Be careful: If you don't use that if(!rows.includes(r)), you could wind up with something like this, depending on what order the user selects those boxes.

//1
//3
//4
//3
//4