The JS Sync Ad Feature allows you to communicate and sync between banners and panels that are served on the same publisher page, even across different ads.

In 2016, I had the opportunity to work on one of the best examples of this for beIN CONNECT. I worked on a 970x250 banner managed with buttons from a 300x250 banner. 

Banner was chosen by Sizmek as the best examples and is still on display as a case study.