Combine data from multiple sheets to 1

combine.gs

// combine data from all sheets in current file
function combineData() {
  // CHANGE SHEET NAME ↓ /////////////////////////////
  var sheetTo = 'combined';
  ////////////////////////////////////////////////////
  var file = SpreadsheetApp.getActiveSpreadsheet();
  var sheets = file.getSheets(); // get all the sheets
  // set where we want to write the results
  var outSheet = file.getSheetByName(sheetTo); 
  var outdata = [], sheet, sName, data = [];
  var maxCols = 0;
  for (i in sheets) { // loop across all the sheets
    var sheet = sheets[i];
    var sName = sheet.getName()
    if (sName !== sheetTo) {
      data = sheet.getDataRange().getValues();
      if (maxCols < (data[0].length+1)) { 
        maxCols = (data[0].length + 1); 
      }
      outdata = outdata.concat(addColumn_(data, sName));
    }
  }
  var normData = fitColumns_(outdata, maxCols);
 write2sheet_({data: normData, sheet: outSheet});
}

// [[a, a, a]] → [[a, a, a, NEW!]]
function addColumn_(data, value) {
  var res = [], row = [];
  for (var i = 0; i < data.length; i++) {
    row = data[i];
    row.push(value);
    res.push(row);
  }
  return res;
}

// [[a, a, a], [a, a, a, a]] → 
// [[a, a, a, ''], [a, a, a, a]]
function fitColumns_(data, numCols) {
  var res = [];
  var row, val;
  for (var i = 0; i < data.length; i++) {
    row = [];
    for (var ii = 0; ii < numCols; ii++) {
      val = data[i][ii] || '';
      row.push(val);
    }
    res.push(row);
  }
  return res;
}

// common writeToSheet Task
// 
// sets (add more to code if needed)
//  sheet: {sheet}
//  data: [[data]]
//  row: N
//  col: N
function write2sheet_(sets) {
  var sheet = sets.sheet;
  if (!sheet) { return -1; }
  var data = sets.data;
  if (!data) { return -2; }
  var row = sets.row || 1;
  var col = sets.col || 1;
  var rows = data.length + row - 1;
  if (!rows || rows < 1) { return -3 }
  var r0 = data[0];
  if (!r0) { return - 4; }
  var cols = r0.length + col - 1;
  if (!cols || cols < 1) { return -5; }
  var r = sheet.getRange(row, col, rows, cols);
  r.setValues(data);
}