update docs & fix type

tsctx · tsctx · commit 0803473b29c6 · 2023-12-20T10:08:41.000+09:00
diff --git a/docs/api/Util.md b/docs/api/Util.md
@@ -10,9 +10,9 @@ Arguments:
 
 - **headers** `Record<string, string | string[]> | (Buffer | string | (Buffer | string)[])[]` (required) - Header object.
 
-- **obj** `Record<string, string | string[]>` (optional) - Object to specify a proxy object. But, if **headers** is an object, it is not used.
+- **obj** `Record<string, string | string[]>` (optional) - Object to specify a proxy object. The parsed value is assigned to this object. But, if **headers** is an object, it is not used.
 
-Returns: `Record<string, string | string[]>`
+Returns: `Record<string, string | string[]>` If **headers** is an object, it is `headers`. Otherwise, if **obj** is specified, it is equivalent to **obj**.
 
 ## `headerNameToString(value)`
 
diff --git a/test/types/util.test-d.ts b/test/types/util.test-d.ts
@@ -10,16 +10,6 @@ expectAssignable<Record<string, string | string[]>>(
   util.parseHeaders({ 'content-type': 'text/plain' }, {})
 );
 
-expectAssignable<Record<string, string | string[]>>(
-  util.parseHeaders(
-    { 'content-type': 'text/plain' },
-    //@ts-ignore
-    {
-      'content-length': 0,
-    }
-  )
-);
-
 expectAssignable<Record<string, string | string[]>>(
   util.parseHeaders({} as Record<string, string> | string[], {})
 );
diff --git a/types/util.d.ts b/types/util.d.ts
@@ -17,21 +17,15 @@ export namespace util {
   /**
    * Receives a header object and returns the parsed value.
    * @param headers Header object
-   * @param obj Object to specify a proxy object. But, if `headers` is an object, it is not used.
+   * @param obj Object to specify a proxy object. Used to assign parsed values. But, if `headers` is an object, it is not used.
+   * @returns If `headers` is an object, it is `headers`. Otherwise, if `obj` is specified, it is equivalent to `obj`.
    */
   export function parseHeaders<
     H extends
       | Record<string, string | string[]>
-      | (Buffer | string | (Buffer | string)[])[],
-    T extends Record<string, unknown>
+      | (Buffer | string | (Buffer | string)[])[]
   >(
     headers: H,
-    obj?: H extends any[] ? T : never
-  ): T extends Record<string, infer V>
-    ? unknown extends V
-      ? Record<string, string | string[]>
-      : H extends any[]
-      ? Record<string, string | string[] | V>
-      : Record<string, string | string[]>
-    : never;
+    obj?: H extends any[] ? Record<string, string | string[]> : never
+  ): Record<string, string | string[]>;
 }
