Inputting an array into Math.Max in Google Apps Scripts

In a Google sheet, I have a custom form based off of some posts/blogs that I have found online to learn more about Google App Scripts. The form works correctly but I am having trouble with the column that should be creating an ID for the row.

From my reading, it seems that my problem is that math.max() takes a list not an array. Furthermore, none of the methods that I found for regular Javascript seem to be working in Google Apps Scripts. Such as, math.max.apply(null,array).

Do I have to iterate the array or is there something to make max() take an array?

Here is the code that I have been playing with.

function itemAdd(form) {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getSheets()[0];
  var sh = SpreadsheetApp.getActiveSheet();
  var lRow = sh.getLastRow();
  var range = sh.getRange(3,1,lRow,1);
  var maxNum = Math.max(range)
  sheet.appendRow([maxNum,form.category, form.item, form.manupub, 
form.details, form.quantity]);
  return true;
}