How can I construct this server backend route?

Question

I'm working on a fullstack project where I need a way to effectuate the following scenario:

Upon a user submit event:

1. A request is posted to the backend
2. When the server receives the req., it begins executing some function
3. The backend should run said function on a loop/indefinitely until the backend receives a subsequent request which instructs the server to cease executing the function after the function completes its current iteration.

I know there must be a way to work this out, but I haven't been able to figure out how to condense my problem/question into something I can google search my way through.

The following will hopefully help to convey what I'm trying to accomplish:

let run_function = false;

app.post('/start', (req, res) => {
  run_function = true;
  while (run_function)
    the_function(req.body);
}

app.get('/stop', (req, res) => {
  run_function = false;
}

Answer 1

Seems like a job for setInterval() / clearInterval()

let handle

// Default 200ms interval
const startLoop = (body, interval = 200) => {
  clearInterval(handle) // stop any previous loops
  handle = setInterval(the_function, interval, body)
}

app.post("/start", (req, res) => {
  startLoop(req.body)
  res.send("Started")
})

app.post("/stop", (req, res) => {
  clearInterval(handle)
  res.send("Stopped")
})

Answer 2

let LoopInterval = null; app.post('/start', (req, res) => { LoopInterval = setInterval(() => { the_function(req.body); }, 0); }); app.get('/stop', (req, res) => { clearInterval(LoopInterval) });