From 23e85e21a50926c48dea4f978e212e4301c20037 Mon Sep 17 00:00:00 2001
From: Evan You <yyx990803@gmail.com>
Date: Wed, 9 Nov 2022 20:50:02 +0800
Subject: [PATCH] fix(watch): ensure oldValue in multi-source watcher is always
 an array

fix #7070
---
 packages/runtime-core/__tests__/apiWatch.spec.ts | 6 +++---
 packages/runtime-core/src/apiWatch.ts            | 2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/runtime-core/__tests__/apiWatch.spec.ts b/packages/runtime-core/__tests__/apiWatch.spec.ts
index c9db3657367..029146b5205 100644
--- a/packages/runtime-core/__tests__/apiWatch.spec.ts
+++ b/packages/runtime-core/__tests__/apiWatch.spec.ts
@@ -183,10 +183,10 @@ describe('api: watch', () => {
     let called = false
     watch(
       [a, b],
-      (newVal, oldVal) => {
+      ([newA, newB], [oldA, oldB]) => {
         called = true
-        expect(newVal).toMatchObject([undefined, undefined])
-        expect(oldVal).toBeUndefined()
+        expect([newA, newB]).toMatchObject([undefined, undefined])
+        expect([oldA, oldB]).toMatchObject([undefined, undefined])
       },
       { immediate: true }
     )
diff --git a/packages/runtime-core/src/apiWatch.ts b/packages/runtime-core/src/apiWatch.ts
index 180843cf745..99445be77d2 100644
--- a/packages/runtime-core/src/apiWatch.ts
+++ b/packages/runtime-core/src/apiWatch.ts
@@ -335,7 +335,7 @@ function doWatch(
           // pass undefined as the old value when it's changed for the first time
           oldValue === INITIAL_WATCHER_VALUE ||
           (isMultiSource && oldValue[0] === INITIAL_WATCHER_VALUE)
-            ? undefined
+            ? []
             : oldValue,
           onCleanup
         ])