type reducer label

Author: Fil

src/reducer.d.ts

@@ -29,8 +29,7 @@ export type ReducerName =
 
 export type ReducerFunction = (values: any[]) => any;
 
-// TODO label
-export type ReducerImplementation<T> =
+export type ReducerImplementation<T> = (
   | {
       reduce: T;
       scale?: Channel["scale"];
@@ -41,7 +40,8 @@ export type ReducerImplementation<T> =
   | {
       reduce(index: number[], values: any[], summary?: any): any;
       scope: "data" | "facet";
-    };
+    }
+) & {label?: string | null};
 
 export type Reducer = ReducerName | ReducerFunction | ReducerImplementation<ReducerName>;