Function root_from_handlevalue 

pub fn root_from_handlevalue<T>(
    v: HandleValue<'_>,
    cx: JSContext,
) -> Result<DomRoot<T>, ()>
where
    T: DomObject + IDLInterface,

Get a DomRoot<T> for a DOM object accessible from a HandleValue. Caller is responsible for throwing a JS exception if needed in case of error.

Safety

cx must point to a valid, non-null JS context.