When does "Start profiling and reload page" decide to stop the automatic recording?

Question

I use the Performance Timeline in Chrome DevTools quite a lot to capture performance recordings of my page.

Most of the time I use the "Start profiling and reload page", which automatically starts and stops the recording.

The question is: When does DevTools decide to stop the recording?

I've noticed that it always continues to record at least a few hundred ms past the "Load"-event and tries to figure out when the page has gone "mostly idle".

But that's quite a fuzzy guess. I'd love to know if it relies on some performance event (like the one used in "time to interactive" in Lighthouse)?

Answer 1

Currently it waits for three seconds after load event.
This is not documented so it may change in the future without notice.

this._millisecondsToRecordAfterLoadEvent = 3000;

---

async _loadEventFired(event) {
  if (this._state !== Timeline.TimelinePanel.State.Recording || !this._recordingPageReload ||
      this._controller.mainTarget() !== event.data.resourceTreeModel.target())
    return;
  const controller = this._controller;
  await new Promise(r => setTimeout(r, this._millisecondsToRecordAfterLoadEvent));

  // Check if we're still in the same recording session.
  if (controller !== this._controller || this._state !== Timeline.TimelinePanel.State.Recording)
    return;
  this._stopRecording();
}