fix: let the refetchInterval function also return undefined

and fall back to false if it does

Author: TkDodo

docs/react/reference/useQuery.md

@@ -101,7 +101,7 @@ const {
 - `queryKeyHashFn: (queryKey: QueryKey) => string`
   - Optional
   - If specified, this function is used to hash the `queryKey` to a string.
-- `refetchInterval: number | false | ((data: TData | undefined, query: Query) => number | false)`
+- `refetchInterval: number | false | ((data: TData | undefined, query: Query) => number | false | undefined)`
   - Optional
   - If set to a number, all queries will continuously refetch at this frequency in milliseconds
   - If set to a function, the function will be executed with the latest data and query to compute a frequency

packages/query-core/src/queryObserver.ts

@@ -342,12 +342,14 @@ export class QueryObserver<
   }
 
   #computeRefetchInterval() {
-    return typeof this.options.refetchInterval === 'function'
-      ? this.options.refetchInterval(
-          this.#currentResult.data,
-          this.#currentQuery,
-        )
-      : this.options.refetchInterval ?? false
+    return (
+      (typeof this.options.refetchInterval === 'function'
+        ? this.options.refetchInterval(
+            this.#currentResult.data,
+            this.#currentQuery,
+          )
+        : this.options.refetchInterval) ?? false
+    )
   }
 
   #updateRefetchInterval(nextInterval: number | false): void {

packages/query-core/src/types.ts

@@ -202,7 +202,7 @@ export interface QueryObserverOptions<
     | ((
         data: TData | undefined,
         query: Query<TQueryFnData, TError, TQueryData, TQueryKey>,
-      ) => number | false)
+      ) => number | false | undefined)
   /**
    * If set to `true`, the query will continue to refetch while their tab/window is in the background.
    * Defaults to `false`.