From c320e5bb7e691b93e0578e7e2304fef31a4f6a4d Mon Sep 17 00:00:00 2001
From: Swaraj Jakanoor <169044732+swaraj792725@users.noreply.github.com>
Date: Sun, 27 Sep 2026 10:58:55 +0530
Subject: [PATCH] fix(utils): handle null and check instanceof safely in
 isJSONSerializable

---
 src/utils.ts       | 21 ++++++++++++++-------
 test/index.test.ts | 21 +++++++++++++++++++++
 2 files changed, 35 insertions(+), 7 deletions(-)

diff --git a/src/utils.ts b/src/utils.ts
index 3bc0dbf5..bad34223 100644
--- a/src/utils.ts
+++ b/src/utils.ts
@@ -18,26 +18,33 @@ export function isJSONSerializable(value: any): boolean {
   if (value === undefined) {
     return false;
   }
+  if (value === null) {
+    return true;
+  }
   const t = typeof value;
-  if (t === "string" || t === "number" || t === "boolean" || t === null) {
+  if (t === "string" || t === "number" || t === "boolean") {
     return true;
   }
   if (t !== "object") {
-    return false; // bigint, function, symbol, undefined
+    return false; // bigint, function, symbol
   }
   if (Array.isArray(value)) {
     return true;
   }
-  if (value.buffer) {
-    return false;
-  }
   // `FormData` and `URLSearchParams` shouldn't have a `toJSON` method,
   // but Bun adds it, which is non-standard.
-  if (value instanceof FormData || value instanceof URLSearchParams) {
+  if (
+    (typeof FormData !== "undefined" && value instanceof FormData) ||
+    (typeof URLSearchParams !== "undefined" && value instanceof URLSearchParams)
+  ) {
+    return false;
+  }
+  if (value.buffer) {
     return false;
   }
   return (
-    (value.constructor && value.constructor.name === "Object") ||
+    !value.constructor ||
+    value.constructor.name === "Object" ||
     typeof value.toJSON === "function"
   );
 }
diff --git a/test/index.test.ts b/test/index.test.ts
index 5ac20b07..671efebf 100644
--- a/test/index.test.ts
+++ b/test/index.test.ts
@@ -525,3 +525,24 @@ describe("ofetch", () => {
     });
   });
 });
+
+describe("isJSONSerializable", () => {
+  it("handles primitives and null safely", async () => {
+    const { isJSONSerializable } = await import("../src/utils.ts");
+    // eslint-disable-next-line unicorn/no-null
+    expect(isJSONSerializable(null)).toBe(true);
+    expect(isJSONSerializable(undefined)).toBe(false);
+    expect(isJSONSerializable("hello")).toBe(true);
+    expect(isJSONSerializable(123)).toBe(true);
+    expect(isJSONSerializable(true)).toBe(true);
+    expect(isJSONSerializable(Symbol("test"))).toBe(false);
+  });
+
+  it("handles objects and special types", async () => {
+    const { isJSONSerializable } = await import("../src/utils.ts");
+    expect(isJSONSerializable({ foo: "bar" })).toBe(true);
+    expect(isJSONSerializable(Object.create(null))).toBe(true);
+    expect(isJSONSerializable(new FormData())).toBe(false);
+    expect(isJSONSerializable(new URLSearchParams())).toBe(false);
+  });
+});