HTMLMediaElement: controller property
Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
Non-standard: This feature is not standardized. We do not recommend using non-standard features in production, as they have limited browser support, and may change or be removed. However, they can be a suitable alternative in specific cases where no standard option exists.
The HTMLMediaElement.controller property represents the media controller assigned to the element.
Value
A MediaController object or null if no media controller is assigned to the element. The default is null.
Specifications
In 2016, the whole Media Controller feature was removed from the HTML specification. It is no longer on track to become a standard.