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"online" event is fired on the <body> of each page when the browser switches between online and offline mode. Additionally, the events bubble up from document.body, to document, ending at window. Both events are non-cancellable (you can't prevent the user from coming online, or going offline).

window.navigator.onLine returns boolean true if the browser is online and false if it is definitely offline (disconnected from the network). The online and offline events are fired when the value of this attribute changes.

It is important to note that this event and attribute are inherently unreliable. A computer can be connected to a network without having Internet access.

You can register listeners for these events in a few familiar ways:

  • using addEventListener on the window, document, or document.body
  • by setting the .ononline or .onoffline properties on document or document.body to a JavaScript Function object. (Note: using window.ononline or window.onoffline will not work for compatibility reasons.)
  • by specifying ononline="..." or onoffline="..." attributes on the <body> tag in the HTML markup.


There's a simple test case that you can run to verify that the events are working.



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