Migrate components to eslint

ts/components/_util.ts

@@ -1,6 +1,4 @@
-// A separate file so this doesn't get picked up by StyleGuidist over real components
-
-import { Ref } from 'react';
+import { MutableRefObject, Ref } from 'react';
 import { isFunction } from 'lodash';
 import memoizee from 'memoizee';
 
@@ -8,6 +6,8 @@ export function cleanId(id: string): string {
   return id.replace(/[^\u0020-\u007e\u00a0-\u00ff]/g, '_');
 }
 
+// Memoizee makes this difficult.
+// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 export const createRefMerger = () =>
   memoizee(
     <T>(...refs: Array<Ref<T>>) => {
@@ -16,8 +16,9 @@ export const createRefMerger = () =>
           if (isFunction(r)) {
             r(t);
           } else if (r) {
-            // @ts-ignore: React's typings for ref objects is annoying
-            r.current = t;
+            // Using a MutableRefObject as intended
+            // eslint-disable-next-line no-param-reassign
+            (r as MutableRefObject<T>).current = t;
           }
         });
       };