How to track an unload event to the iframe?

There is a page. It has iframe. In the iframe loaded a page of the e-signature service. After the user has signed the document in the uploaded service, the service closes its window, and the user continues to stare at a blank iframe.

Question: How to track the unload event of the page from iframe to this event to hide the frame (or perform another action)?

Welcome any options.
June 14th 19 at 20:29
1 answer
June 14th 19 at 20:31
Look at the content of the frame timer and display the desired content, stop the timer and perform the desired functions?

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