Google Sheets – Filling Columns with Formulas Without Dragging

You can't really have "variables" in a spreadsheet; it's not a programming language. The values are contained in cells and can be referred to by location, possibly relative to location of other cells. If cells get rearranged so that the relations within rows or columns are lost, that is already a problem.

In your example, you want to refer to Count of Bananas in a way that is independent of sorting. The function vlookup does this nicely:

=vlookup("Banana", A:B, 2, False)

This means: get the value in column B that's in the row with "Banana".

Of course, if you sort column B but not column A, this is going to break; but then the entire logic of Fruit/Count columns is broken.

Instead of getFormulas and setFormulas, use copyTo method:

range.copyTo(newRange);

This will have the same effect as if you selected the last row and copied it below. In particular, it will also copy down any values that were entered directly into cells. If you prefer such values to not be copied, use getFormulas/setFormulas combination on newRange:

range.copyTo(newRange);
newRange.setFormulas(newRange.getFormulas());

The effect of the last line: no change of formulas, but the cells that didn't contain a formula will become empty.

R1C1 approach

You can also try replacing the last three rows of addRow with

var formulas = range.getFormulasR1C1();
var newRange = sh.getRange(lRow+1,1,1,lCol);
newRange.setFormulasR1C1(formulas);

This will make sure the references in formulas are remapped as if you copy-pasted them. However, this has a major limitation: setFormulasR1C1 doesn't work correctly with empty string as its argument, which will result in #ERROR! messages in the cells that should be left blank.

The reason R1C1 works differently is that getFormulasR1C1 retrieves formulas in a relative form: for example, a reference from A3 to D2 becomes R[-1]C[3], meaning "one row up, three columns to the right". When the formula is set to, for example, E4 with setFormulasR1C1, the cell reference will appear as H3.