By using the “unload” event in JavaScript you are able to detect when the window has closed. In the case of an iframe, it is possible to detect when the src attribute has been removed or changed.

In this video we take a look at an example of the “unload” event in the case of an iframe, where we send a message to the parent window when the child window (within the iframe) gets un-loaded.

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For your reference, check this out:
https://developer.mozilla.org/en-US/docs/Web/Events/unload

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