An API which allows posting of tasks which are scheduled during periods when the browser is idle, and are passed a deadline when called which is calculated based on how long the browser expects to remain idle. This enables developers to perform background work on the main event loop, without impacting latency-critical events such as animation and input response.
Docs: https://developer.mozilla.org/en-US/docs/Web/API/Window/requestIdleCallback https://developer.mozilla.org/en-US/docs/Web/API/Window/cancelIdleCallback https://developers.google.com/web/updates/2015/08/using-requestidlecallback
Samples: https://developers.google.com/web/updates/2015/08/using-requestidlecallback