These APIs

are disabled when the page is not visible: Geolocation, Vibration, Device

Motion. The goal is to save battery and CPU.

A tab is eligible for napping when it meets any of the following conditions:

The tab is in the background.

The browser window is minimized.

The browser window is in a desktop space not currently displayed.

The browser window is occluded (covered) by another window or other object on the screen.

The browser window is idle (has not been updated recently).

The screen saver is on.

Napping is inhibited when a tab is engaged in useful nonvisual tasks such as playing audio or dynamically loading content.

A pair of new properties on the document object allow a page to determine when it is not visible to the user, so that it can avoid unnecessary processing and minimize power consumption:

document.hidden: A Boolean flag telling whether the document is currently hidden.

document.visibilityState: A string denoting the document’s current visibility state. Possible values are:

"hidden": The document is currently hidden.

"visible": The document is currently visible.

"prerender": The document’s contents are currently being preloaded but not yet rendered. This occurs, for instance, when the user begins typing a URL into the browser’s location field: the browser attempts to predict the most likely completion of the partial URL as it is typed and begins preloading the predicted page so that it will be ready for immediate rendering when the Return key is pressed.

A new event type, visibilitychange, notifies the application when the page’s visibility state has changed. The application can install an event listener that tests the values of the properties above and responds accordingly.