Submitting data to google sheet with multiple tab sheets - ajax

Question

I'm referencing this article "How to Submit an HTML Form to Google Sheets…without Google Forms", it worked perfectly for me for only a Google Sheet with one tab.
Need help how to dynamically select what sheet tab the data should be written in the case the google sheet has multiple tabs. I'm using Ajax to submit google sheet btw.
Here's the call by the Ajax:
var $form = $('form#test-form'),
url = 'https://script.google.com/macros/s/MyScript/exec'
$('#submit-form').on('click', function(e) {
e.preventDefault();
var jqxhr = $.ajax({
url: url,
method: "GET",
dataType: "json",
data: $form.serializeObject()
}).success(
// do something
);
})
The code on google sheet web app
function doGet(e){
return handleResponse(e);
}
// Enter sheet name where data is to be written below
var SHEET_NAME = "Sheet1";
var SCRIPT_PROP = PropertiesService.getScriptProperties(); // new property service
function handleResponse(e) {
// shortly after my original solution Google announced the LockService[1]
// this prevents concurrent access overwritting data
// [1] http://googleappsdeveloper.blogspot.co.uk/2011/10/concurrency-and-google-apps-script.html
// we want a public lock, one that locks for all invocations
var lock = LockService.getPublicLock();
lock.waitLock(30000); // wait 30 seconds before conceding defeat.
try {
// next set where we write the data - you could write to multiple/alternate destinations
var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
var sheet = doc.getSheetByName(SHEET_NAME);
// we'll assume header is in row 1 but you can override with header_row in GET/POST data
var headRow = e.parameter.header_row || 1;
var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
var nextRow = sheet.getLastRow()+1; // get next row
var row = [];
// loop through the header columns
for (i in headers){
if (headers[i] == "Timestamp"){ // special case if you include a 'Timestamp' column
row.push(new Date());
} else { // else use header name to get data
row.push(e.parameter[headers[i]]);
}
}
// more efficient to set values as [][] array than individually
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 lock
lock.releaseLock();
}
}
function setup() {
var doc = SpreadsheetApp.getActiveSpreadsheet();
SCRIPT_PROP.setProperty("key", doc.getId());
}
If there is a way to change the variable SHEET_NAME dynamically then I think it will be good. Thanks