How to kill spawn program nodejs based on button in frontend - node.js

Question

In the backend, I run a script when user clicks button however, I need the ability for frontend to be able to click button to stop the script. I am using eventSource on the frontend to stream the output of the script to the frontend. I have tried spawn.kill(), kill(), and everything. I can't seem to get it to stop the script. The script still continues even though i close the eventSource and call spw.kill() in the res.socket.on function. Any help will be appreciated!
Frontend code here
const fetchStream = (e) => {
e.preventDefault();
var evtSource = new EventSource(
`http://${process.env.REACT_APP_IP_ADDRESS}/run`
);
evtSource.onmessage = function (e) {
var d = Date.now();
var formatteddatestr = String(moment(d).format("M/D/YYYY-hh:mm:ss a"));
setData((data) => [...data, formatteddatestr + ": " + e.data]);
if (stopTest) {
// I have a button that turns this to true when user clicks it.
evtSource.close();
setStopTest(false);
setData((data) => []);
setRunning(false);
}
if (e.data.includes("Test done.")) {
evtSource.close();
createPDF(e);
}
};
evtSource.onerror = function (e) {
evtSource.close();
setRunning(false);
};
This is backend code
router.get("/", function (req, res) {
res.writeHead(200, {
"Content-Type": "text/event-stream",
"Cache-control": "no-cache",
// Connection: "keep-alive",
});
// res.write("\n");
var d = new Date(Date.now());
var formatteddatestr = String(moment(d).format("M/D/YYYY-hh:mm:ss a"));
fs.writeFileSync(__dirname + "/start.txt", formatteddatestr);
var spw = spawn("./Validator", ["-d", "tests"], {
cwd: __dirname + "/../../../Validator",
detached: true,
}),
str = "";
var kill = false;
res.socket.on("end", (e) => {
// doesn't work here
// code gets here when user clicks button to stop script
spw.kill();
res.end();
});
spw.stdout.on("data", function (data) {
res.write("data: " + data + "\n\n");
});
spw.stderr.on("data", function (data) {
//works here
spw.kill();
});
});