fix(destroy): handle previously set cookies

before this commit, when using destroy(), previously set cookies would be
ignored

fixes #229

lib/index.js

@@ -77,7 +77,8 @@ export async function applySession(
         ...cookieOptions,
         maxAge: 0,
       });
-      res.setHeader("set-cookie", [cookieValue]);
+      const existingSetCookie = [res.getHeader("set-cookie") || []].flat();
+      res.setHeader("set-cookie", [...existingSetCookie, cookieValue]);
     },
   };
 

lib/index.test.js

@@ -276,6 +276,7 @@ test("req.session.destroy", () => {
       },
       {
         setHeader: jest.fn(),
+        getHeader: jest.fn(),
       },
     );
   });
@@ -647,7 +648,7 @@ test("it handles previously set cookies (single value)", () => {
   });
 });
 
-test("it handles previously set cookies (multiple values)", () => {
+test("it handles previously set cookies (multiple values) on save()", () => {
   return new Promise((done) => {
     const handler = async (req, res) => {
       await req.session.save();
@@ -672,3 +673,35 @@ test("it handles previously set cookies (multiple values)", () => {
     );
   });
 });
+
+test("it handles previously set cookies (multiple values) on destroy()", () => {
+  return new Promise((done) => {
+    const handler = async (req, res) => {
+      await req.session.destroy();
+
+      expect(res.setHeader.mock.calls[0]).toMatchInlineSnapshot(`
+        Array [
+          "set-cookie",
+          Array [
+            "existingCookie=value",
+            "anotherCookie=value2",
+            "test=; Max-Age=0; Path=/; HttpOnly; Secure; SameSite=Lax",
+          ],
+        ]
+      `);
+      done();
+    };
+    const wrappedHandler = withIronSession(handler, { password, cookieName });
+    wrappedHandler(
+      {
+        headers: { cookie: "" },
+      },
+      {
+        setHeader: jest.fn(),
+        getHeader: function () {
+          return ["existingCookie=value", "anotherCookie=value2"];
+        },
+      },
+    );
+  });
+});