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document.onvisibilitychange

The Document.onvisibilitychange property represents the event handler that is called when a visibilitychange event reaches this object.

obj.onvisibilitychange = function;

function is the name of a user-defined function, without the () suffix or any parameters, or an anonymous function declaration.

document.onvisibilitychange = function() { 
  console.log("Visibility of page has changed!");
};

Specification	Status	Comment
Page Visibility (Second Edition) The definition of 'onvisibilitychange' in that specification.	Recommendation	Initial definition.

	Desktop
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari
Basic support	33 33 13 Prefixed Prefixed Requires the vendor prefix: webkit	Yes	56	10	12.1 12.1 Doesn't fire the `visibilitychange` event when the browser window is minimized, nor when `hidden` is set to true.	7

	Mobile
	Android webview	Chrome for Android	Edge Mobile	Firefox for Android	Opera for Android	iOS Safari	Samsung Internet
Basic support	4.4.3	33	Yes	56	12.1 12.1 Doesn't fire the `visibilitychange` event when the browser window is minimized, nor when `hidden` is set to true.	7	?