Please note that this feature is only for publishers using Google Ad Manager tags. When you are using Google Publisher Tags (GPT), your ads will automatically load into iframes.
Instead of JavaScript, you can use iframe tagging, which is available upon request. With iframe tagging, you'll define ad units only in the FillSlot calls, not in the header of the page. Also, iframe tags will load independently of page content so your ads won't have to wait for your page to load before being displayed.
Using iframe tags may cause conflicts with rich media, AdSense, and page formatting. For assistance with iframe tags, please contact us.
For more information on iframe tags, see Use iframe tags.