Get URL parameter passed to google form via apps script - google-apps-script

Question

I`m trying to get URL parameter passed to google form via apps script, but don't know exactly how does it does. Case:
https://docs.google.com/forms/d/e/XXXX/viewform?a=12
(Passed XXXX, cause this form is for clients use)
and I need to get answers and this parameter after submit.
function onSubmit(e) {
var POST_UR​L = "www.myserver.com?id=a";//this parametr
var form = FormApp.getActiveForm();
var allResponses = form.getResponses();
var latestResponse = allResponses[allResponses.length - 1];
var response = latestResponse.getItemResponses();
var payload = {};
for (var i = 0; i < response.length; i++) {
var question = response[i].getItem().getTitle();
var answer = response[i].getResponse();
payload[question] = answer;
}
var options = {
"method": "post",
"contentType": "application/json",
"payload": JSON.stringify(payload)
};
UrlFetchApp.fetch(POST_URL, options);
};
​​
This code made for sending POST request with answers of form to my server and how can I pass the ​a=12 or only 12 to this request?

Answer 1

You need to append the values to POST_URL instead of passing via payload. There's a nice bit of code provided by Google in their OAuth2 library that will do this for you:
/**
* Builds a complete URL from a base URL and a map of URL parameters.
* #param {string} url The base URL.
* #param {Object.<string, string>} params The URL parameters and values.
* #return {string} The complete URL.
* #private
*/
function buildUrl_(url, params) {
var paramString = Object.keys(params).map(function(key) {
return encodeURIComponent(key) + '=' + encodeURIComponent(params[key]);
}).join('&');
return url + (url.indexOf('?') >= 0 ? '&' : '?') + paramString;
}
Which means you can do something like:
var POST_URL = "www.myserver.com?id=a";
var payload = {a: 12};
console.log(buildUrl_(POST_URL, payload)); // www.myserver.com?id=a&a=12
function buildUrl_(url, params) {
var paramString = Object.keys(params).map(function(key) {
return encodeURIComponent(key) + '=' + encodeURIComponent(params[key]);
}).join('&');
return url + (url.indexOf('?') >= 0 ? '&' : '?') + paramString;
}
Ultimately, the final line in your code would be:
UrlFetchApp.fetch(buildUrl_(POST_URL, payload), options);