Stopping an async function without waiting for it to finish - node.js

Question

In my system there is an updater function running every few seconds, this function looks something like this:
function updater() {
this.updater = setTimeout(async function() {
let data = await updatingFromInternet(url);
updater();
}, 5000);
}
I call the updater function once and it should update and run itself again 5 seconds after it last updated.
Since the updatingFromInternet function is an async function I can only wait for it to finish and then decide whether or not to keep updating but not stop it at the point it is currently waiting (fetching internet data).
Is there a simple way to stop the update immediately without the need to wait for the async function to return?

Answer 1

Yes as long as you have a reference to the timer handle:
clearTimeout(this.updater)

Answer 2

Instead of updater being a function, I would make it an object. Even with a cancellation featrue, if you called the updater function before the previous one was cancelled, this.updater would be overwritten and you couldn't cancel that timer, it would continue forever.
The below example uses an IIFE to encapsulate its variables and returns an object with a start and stop method.
const elOutput = document.getElementById('output'),
elStatus = document.getElementById('status');
const url = '';
// IIFE that returns the updater object
const updater = (function () {
let timer = null;
let update = function () {
timer = setTimeout(async () => {
elStatus.textContent = 'Waiting for data...';
let data = await updatingFromInternet(url);
// if timer has been set to null, updates have been
// cancelled
if (timer !== null) {
// do something with data here
elOutput.textContent = data;
elStatus.textContent = 'Updating...';
update();
}
}, 5000);
};
let start = () => {
// if the timer is not already running...
if (timer === null) {
elStatus.textContent = 'Starting update timer...';
update();
}
};
let stop = () => {
clearTimeout(timer);
timer = null;
elStatus.textContent = 'Updates Canceled';
};
// return our updater object with its start and stop methods
return {
start,
stop
};
}());
document.getElementById('update').addEventListener('click', updater.start, false);
document.getElementById('cancel').addEventListener('click', updater.stop, false);
// mocking a networks response
const updatingFromInternet = (function () {
let counter = 0;
return function (url) {
return new Promise((res, rej) => {
setTimeout(res.bind(null, counter++), 1000);
});
};
}());
<button type="button" id="update">Update</button>
<button type="button" id="cancel">Cancel updates</button>
<div id="output"></div>
<div id="status"></div>
Even better, since you are using Node, this is the sort of thing that would be ideal to put in a module.
// updater.js
let updatingFromInternet = require('./updatingFromInternet.js');
let timer = null;
let callback = null;
let update = function () {
timer = setTimeout(async () => {
let data = await updatingFromInternet(url);
// if timer has been set to null, updates have been
// cancelled
if (timer !== null) {
callback(data);
update();
}
}, 5000);
};
let start = (userCallback) => {
// if the timer is not already running
// and we received a callback function
if (timer === null && typeof userCallback === 'function') {
callback = userCallback;
update();
}
};
let stop = () => {
clearTimeout(timer);
timer = null;
};
module.exports = {
start,
stop
};
Then, to use it, require it in your main file:
let updater = require('./updater.js');
updater(function (data) {
console.log(data);
}