Assigning value to new objects made using constructors

Question

I have just started writing JS for Google Apps Scripts to automate some of my Google Sheets. So my apologies in advance if there is an obvious error.

I have defined an object using constructor, when I try to make new objects of the same type giving the variable values in round brackets those values do seem to be taken.

Here's the code:

var sheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("First Sorting");
var negsheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("Negative List");
function pastesheet (lastrow, append, pasterow) {
  this.lastrow = sheet.getLastRow();
  this.append = 1;
  this.pasterow = sheet.getRange(1, 1);
}
var neg = new pastesheet(negsheet.getLastRow(), 1, negsheet.getRange(1, 1));

From logger I observed that using the above code neg.lastrow actually refers to the last row of sheet "First Sorting" and not "Negative List" that I want it to refer to. I also observed that the following tweak to the last line of above code does what I want:

ver neg = new pastesheet();
neg.lastrow = negsheet.getLastRow();
neg.append = 1;
neg.pastrow = negsheet.getRange(1,1)

However, I would really like to know what am I doing wrong in the first instance? It is quite convenient to assign everything in one line and I plan to do this for quite a few sheets.

Answer 1

Your constructor is referencing sheet which is not an argument and thus references the "First Sorting" sheet defined in the global body.

Did you intend to do something along these lines:

function pastesheet (sheet, append) {
  this.lastrow = sheet.getLastRow();
  this.append = append;
  this.pasterow = sheet.getRange(1, 1);
}
var neg = new pastesheet(negsheet, 1);

?