class DataPoller {
constructor(url) {
this.url = url;
this.data = null;
}
startPolling(interval = 1000) {
setInterval(async () => {
const res = await fetch(this.url);
this.data = await res.json();
console.log('Updated:', this.data);
}, interval);
}
stopPolling() {
// ??? — no way to stop it
}
}
const poller = new DataPoller('/api/status');
poller.startPolling(); // interval #1
poller.startPolling(); // interval #2 — #1 still running!class DataPoller {
constructor(url) {
this.url = url;
this.data = null;
this._intervalId = null;
}
startPolling(interval = 1000) {
this.stopPolling(); // clear any existing interval first
this._intervalId = setInterval(async () => {
const res = await fetch(this.url);
this.data = await res.json();
console.log('Updated:', this.data);
}, interval);
}
stopPolling() {
if (this._intervalId !== null) {
clearInterval(this._intervalId);
this._intervalId = null;
}
}
}Bug: setInterval returns an ID needed for clearInterval. Without storing it, you can never cancel the interval. Each startPolling() call piles up another interval.
Explanation: Store the interval ID and clear it before creating a new one. stopPolling() uses the stored ID to call clearInterval. Guards with !== null for safety.
Key Insight: Every setInterval must have a corresponding clearInterval. Always store the ID. Clear before re-creating to avoid accumulating intervals.