How to avoid re-start function in the script, which is working with iframe?

There is a page which adds a call to a js script, it adds to the iframe tag. After adding it the script again. I need to enter a function that will run once. the flag doesn't work because the variable is overridden. The listener for downloading iframe is activated every time when you change the page inside iframe.

https://jsfiddle.net/zrkq9gs8/2/
April 3rd 20 at 17:20
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