Injecting functionality into a page displayed in an iframe?

I want to show a page inside of an iframe, it will be running on the same server as my application, I want to fire an event whenever a certain page appears by locating an element on the page and then add a button next to that element with some functionality. Is that feasable? how would I put an event on the iframe so that whenever an item with that class is created it runs my code?
 
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