2D Dependent Dropdowns for Google Sheets. ~70 lines of code. Classy sample

Dependent DropDowns 2D Wide. v0.gs

// Copy sample file here:
// https://docs.google.com/spreadsheets/d/1hUOuDZcfXxaLvJbEA-SxzF4oGGU3lW3iJyS4wAV8YWA/copy

function onEdit(e) {
   dvl0_(e);
}

function dvl0_sets_() {
  return [
    {
      lib: {
        'Materials':                       "'lists'!A2:A",
        'Services':                        "'lists'!B2:B",
        'Outsource':                       "'lists'!C2:C",
        'Production costs':                "'lists'!D2:D"
      },
      sheet: "main",
      row: 2,
      col1: 3,
      col2: 4 
    }
  ];
}


function dvl0_(e) {
  var sets = dvl0_sets_();
  var res = [], res0;
  for (var i = 0; i < sets.length; i++) {
    res0 = dvl0_run_(sets[i], e);
    res.push(res0);
  }
  console.log(res);
}


function dvl0_run_(ini, e) {
  var f = SpreadsheetApp.getActive();
  var r = e.range;
  var s = r.getSheet();
  if (s.getName() !== ini.sheet) {
    return 'wrong sheet';
  }
  var val = e.value;
  if (!val) {
    return 'no value';
  }
  var col = r.getColumn();
  if (col !== ini.col1) {
    return 'wrong column';
  }
  var row = r.getRow();
  if (row < ini.row) {
    return 'wrong row';
  }
  var lib = ini.lib;
  var rA1 = lib[val];
  if (!rA1) {
    var message = 'not found in lib'
    f.toast(message);
    return message;
  }
  var rTo = s.getRange(row, ini.col2);
  var rule = SpreadsheetApp.newDataValidation().
    requireValueInRange(f.getRange(rA1));
  rTo.setDataValidation(rule);
  return 'success!'
}