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var SHEET_NAME = "Sheet1"; //  Enter sheet name where results will be collected
var CHOICES_SHEET_NAME = "Choices"; //We will use it later

var SCRIPT_PROP = PropertiesService.getScriptProperties(); // new property service

//We will utilise GET method later
// function doGet(e){
//   return handleResponse(e);
// }

function doPost(e){
	return handleResponse(e);
}

function handleResponse(e) {
	// The LockService allows you to have only one invocation of the script or portions thereof run at a time.
	// More about: http://googleappsdeveloper.blogspot.co.uk/2011/10/concurrency-and-google-apps-script.html
	var lock = LockService.getPublicLock(); //Public lock locks for any invocation of script.
	lock.waitLock(30000);

	try {
		// Alternatively, you can hard code spreadsheet here
		// eg. SpreadsheetApp.openById("1AcsuboS3xxk0kj02ACcE_j4ASb8GrxyZscTU5IM-wqc")
		var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
		var sheet = doc.getSheetByName(SHEET_NAME);

		var data = JSON.parse(e.postData.contents);

		var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
		var nextRow = sheet.getLastRow()+1; // get next row
		var row = [];

		for (i in headers){
			if (headers[i] == "datetime"){
				row.push(new Date());
			} 

			else if (headers[i] == "raw_data"){
				row.push(JSON.stringify(data));
			}
			
			else {
				//To support multiple choice question (checkboxes)
				if(Array.isArray(data[headers[i]])) {
					row.push(data[headers[i]].join('|'));
				}else {
					row.push(data[headers[i]]);
				}
				//TODO: Support other types of questions
			}
		}

		sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
		// return json success results
		return ContentService
			.createTextOutput(JSON.stringify({"result":"success", "row": nextRow}))
			.setMimeType(ContentService.MimeType.JSON);
	} catch (e){
		// if error return this
		return ContentService
			.createTextOutput(JSON.stringify({"result":"error", "error": e}))
			.setMimeType(ContentService.MimeType.JSON);
	} finally {
		//Release public lock from line 19
		lock.releaseLock();
	}
}

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

Gist for the article:
How to create online survey for free with SurveyJS and Google Sheets