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 non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.
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.