fix(flatMap): should infer return type correctly without depth prop (#…

…809) * fix(flatMap): should infer return type correctly without depth prop * fix
toss · Nov 12, 2024 · 674a795 · 674a795
1 parent d76172a
commit 674a795
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Showing 3 changed files with 10 additions and 3 deletions.
diff --git a/package.json b/package.json
@@ -195,4 +195,4 @@
     "format": "prettier --write .",
     "transform": "jscodeshift -t ./.scripts/tests/transform-lodash-test.ts $0 && prettier --write $0"
   }
-}
+}
diff --git a/src/array/flatMap.spec.ts b/src/array/flatMap.spec.ts
@@ -33,4 +33,11 @@ describe('flatMap', () => {
     const result = flatMap(emptyArr, item => [item, item]);
     expect(result).toEqual([]);
   });
+
+  it('should return type is flatten array without depth prop', () => {
+    const arr: string[] = ['1', '2'];
+    const result = flatMap(arr, item => [item, item]);
+    expect(result).toEqual(['1', '1', '2', '2']);
+    result[0].substring(0, 1);
+  });
 });
diff --git a/src/array/flatMap.ts b/src/array/flatMap.ts
@@ -20,10 +20,10 @@ import { flatten } from './flatten.ts';
  * flatMap(arr, (item: number) => [[item, item]], 2);
  * // [1, 1, 2, 2, 3, 3]
  */
-export function flatMap<T, U, D extends number>(
+export function flatMap<T, U, D extends number = 1>(
   arr: readonly T[],
   iteratee: (item: T) => U,
-  depth = 1 as D
+  depth: D = 1 as D
 ): Array<FlatArray<U[], D>> {
   return flatten(
     arr.map(item => iteratee(item)),