docs(types): clarify ExistsFunction note re: narrowing through wrappers

adrai · adrai · commit 8fec684b4e56 · 2026-05-08T06:51:56.000+02:00
diff --git a/index.d.ts b/index.d.ts
@@ -215,9 +215,13 @@ export type Callback = (error: any, t: TFunction) => void;
  *
  * Note: this shape intentionally does not include a type-guard overload so it
  * remains easy to assign arrow functions to. The type guard narrowing to
- * {@link SelectorKey} is declared directly on `i18n.exists` instead.
- * Users who want narrowing on a custom wrapper can type it as
- * `typeof i18next.exists`.
+ * {@link SelectorKey} is declared directly on `i18n.exists` instead. If you
+ * need narrowing in your own code, call `i18next.exists` directly or forward
+ * the function by reference (e.g. `const exists: typeof i18next.exists =
+ * i18next.exists`). Wrapping it in an arrow function will lose the narrowing —
+ * there is currently no way to keep type-guard narrowing through an
+ * arrow-function wrapper, which is why `ExistsFunction` deliberately omits the
+ * predicate overload.
  */
 export interface ExistsFunction<
   TKeys extends string = string,
