Includes: Fix false-positive when the array contains null and you…

… are checking against `undefined` (#413)
sindresorhus · Jul 2, 2022 · de5e7fc · de5e7fc
1 parent 96fe795
commit de5e7fc
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Showing 2 changed files with 11 additions and 5 deletions.
diff --git a/source/includes.d.ts b/source/includes.d.ts
@@ -15,8 +15,8 @@ type hasRed<array extends any[]> = Includes<array, 'red'>;
 @category Array
 */
 export type Includes<Value extends readonly any[], Item> =
-	IsEqual<Value[0], Item> extends true
-		? true
-		: Value extends [Value[0], ...infer rest]
-			? Includes<rest, Item>
-			: false;
+	Value extends readonly [Value[0], ...infer rest]
+		? IsEqual<Value[0], Item> extends true
+			? true
+			: Includes<rest, Item>
+		: false;
diff --git a/test-d/includes.ts b/test-d/includes.ts
@@ -32,6 +32,12 @@ expectType<false>(objectIncludes);
 const objectIncludesPass: Includes<[{a: 1}], {a: 1}> = true;
 expectType<true>(objectIncludesPass);
 
+const nullIncludesUndefined: Includes<[null], undefined> = false;
+expectType<false>(nullIncludesUndefined);
+
+const nullIncludesNullPass: Includes<[null], null> = true;
+expectType<true>(nullIncludesNullPass);
+
 declare const anything: any;
 
 expectError<Includes>(anything);