From d7d408ab6c8ccdcfb990231c53a9d0621bb75ce0 Mon Sep 17 00:00:00 2001
From: Shaurya Singh <sshaurya914@gmail.com>
Date: Thu, 4 Jun 2026 16:30:49 -0700
Subject: [PATCH] fix(utils.url): delete existing key before appending array
 values in withQuery

When withQuery merges a query object into a URL that already has an
existing query string, scalar values are correctly replaced via
searchParams.set(). Array values, however, were appended without first
deleting the existing key for that name, so the old value would persist
alongside the new ones.

For example:
  withQuery('https://example.org/path?tag=old', { tag: ['a', 'b'] })
  produced:  ...?tag=old&tag=a&tag=b   (wrong)
  now gives: ...?tag=a&tag=b           (correct)

Add searchParams.delete(key) before the append loop to match the
replace semantics that searchParams.set() already provides for
scalar values.
---
 src/utils.url.ts   |  1 +
 test/index.test.ts | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/src/utils.url.ts b/src/utils.url.ts
index 5a725353..610ed852 100644
--- a/src/utils.url.ts
+++ b/src/utils.url.ts
@@ -90,6 +90,7 @@ export function withQuery(input: string, query?: QueryObject): string {
     if (value === undefined) {
       searchParams.delete(key);
     } else if (Array.isArray(value)) {
+      searchParams.delete(key);
       for (const item of value) {
         searchParams.append(key, normalizeQueryValue(item));
       }
diff --git a/test/index.test.ts b/test/index.test.ts
index 5ac20b07..e8b86e3a 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -344,6 +344,20 @@ describe("ofetch", () => {
     });
   });
 
+  it("replaces existing array query params instead of accumulating", async () => {
+    // When the URL already carries a value for a key and the query option
+    // supplies an array for that same key, the existing value should be
+    // replaced, not accumulated alongside the new ones. The /url/** endpoint
+    // echoes the raw path+search so we can inspect all repeated values.
+    const result = await $fetch(getURL("url/check?tag=old&other=1"), {
+      query: { tag: ["a", "b"] },
+    });
+    // "tag=old" must not appear; only "tag=a" and "tag=b" should be present
+    expect(result).toContain("tag=a");
+    expect(result).toContain("tag=b");
+    expect(result).not.toContain("tag=old");
+  });
+
   it("deep merges defaultOptions", async () => {
     const _customFetch = $fetch.create({
       query: {