ajax完成后，在js内加载iframe或div

On my site ajax calling iframe that is loading some sort of data. I want to load the iframe or div data as soon as the ajax request completes or data is loaded. I cannot access ajax directly, so I am trying it this way, but it is showing undefined. I think this is due to the iframe or div not loading each time. Any help with how I can load the iframe or div inside js without touching ajax code.Thanks that is loading