Google Drive – List all files id inside a folder (no subfolders)

If you want to list in a spreadsheet all files id that are located inside a folder (no subfolders).

function list_all_files_inside_a_folder(){
  var sh = SpreadsheetApp.getActiveSheet();
  var folder = DriveApp.getFolderById('1a1SkFgbMIr_8z1HnZvIpUPcOQ0NWp3HL'); //Change the folder ID here 
  var list = [];
  sh.clear();
  list.push(['File Name','File ID','Size(MB)']);
  var files = folder.getFiles();
  while (files.hasNext()){
    file = files.next();
    var row = []
    row.push(file.getName(),file.getId(),file.getSize()/1048576)
    list.push(row);
  }
   sh.getRange(1,1,list.length,list[0].length).setValues(list);
}