Google Spreadsheets Script

//  1. Run > setup
//
//  2. Publish > Deploy as web app
//    - enter Project Version name and click 'Save New Version'
//    - set security level and enable service (execute as 'me' and access 'anyone, even anonymously)
//
//  3. Copy the 'Current web app URL' and post this in your form/script action
//
//  4. Insert column names on your destination sheet matching the parameter names of the data you are passing in (exactly matching case)

var SCRIPT_PROP = PropertiesService.getScriptProperties();

function doGet(e){
  try {
    var key = e.parameter["key"]
    var sheetName = e.parameter["sheet"]
    var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
    var sheet = doc.getSheetByName(e.parameter["sheet"]);
    var data = sheet.getDataRange().getValues();
    var value
    for (var i = 1; i < data.length; i++) {
      if (data[i][0] == key) {
        value = data[i][1];
      }
    }
    if (value){
      return ContentService
      .createTextOutput(JSON.stringify({"result":"success", "value": value}))
      .setMimeType(ContentService.MimeType.JSON);
    } else {
      return ContentService
      .createTextOutput(JSON.stringify({"result":"error", "error": "Key not found"}))
      .setMimeType(ContentService.MimeType.JSON);
    }
  } catch(e){
    return ContentService
          .createTextOutput(JSON.stringify({"result":"error", "error": "Database does not exist"}))
          .setMimeType(ContentService.MimeType.JSON);
  }
}

function doPost(e){
  var sheetNom = e.parameter["sheet"];
  var lock = LockService.getPublicLock();
  lock.waitLock(30000);
  try {
    var key = e.parameter["key"]
    var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
    var sheet = doc.getSheetByName(e.parameter["sheet"]);
    var data = sheet.getDataRange().getValues();
    var headRow = e.parameter.header_row || 1;
    var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    var nextRow = sheet.getLastRow()+1;
    var row = [];
    for (var i = 1; i < data.length; i++) {
      if (data[i][0] == e.parameter["key"]) {
        nextRow = i + 1;
      }
    }
    for (i in headers){
        row.push(e.parameter[headers[i]]);
    }
    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
    return ContentService
          .createTextOutput(JSON.stringify({"result":"success", "row": nextRow}))
          .setMimeType(ContentService.MimeType.JSON);
  } catch(e){
    return ContentService
    .createTextOutput(JSON.stringify({"result":"error", "error": e, "test": "Test", "sheet": sheetNom}))
          .setMimeType(ContentService.MimeType.JSON);
  } finally {
    lock.releaseLock();
  }
}

function setup() {
    var doc = SpreadsheetApp.getActiveSpreadsheet();
    SCRIPT_PROP.setProperty("key", doc.getId());
}