main.gs

function doPost(e) {
  try {
    Logger.log(e);
    record_data(e);

    return ContentService
    .createTextOutput(
      JSON.stringify({
        "result":"success",
        "data": JSON.stringify(e.parameters)
      })
    )
    .setMimeType(ContentService.MimeType.JSON);
  } catch(error) {
    Logger.log(error);
    return ContentService
    .createTextOutput(JSON.stringify({"result":"error", "error": e}))
    .setMimeType(ContentService.MimeType.JSON);
  }
}

function record_data(e) {
  Logger.log(JSON.stringify(e)); // log the POST data in case we need to debug it
  try {
    var doc     = SpreadsheetApp.getActiveSpreadsheet();
    var sheet   = doc.getSheetByName('responses'); // select the responses sheet
    var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    var nextRow = sheet.getLastRow()+1; // get next row
    var row     = [ new Date() ]; // first element in the row should always be a timestamp
    // loop through the header columns
    for (var i = 1; i < headers.length; i++) { // start at 1 to avoid Timestamp column
      if(headers[i].length > 0) {
        row.push(e.parameter[headers[i]]); // add data to row
      }
    }
    // more efficient to set values as [][] array than individually
    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
  }
  catch(error) {
    Logger.log(e);
  }
  finally {
    return;
  }
}