fix(reactivity): call array subclass methods (#3624)

fix #2314, close #2315

packages/reactivity/__tests__/reactiveArray.spec.ts

@@ -171,4 +171,45 @@ describe('reactivity/reactive/Array', () => {
       expect(original.indexOf(ref)).toBe(1)
     })
   })
+
+  describe('Array subclasses', () => {
+    class SubArray<T> extends Array<T> {
+      lastPushed: undefined | T
+      lastSearched: undefined | T
+
+      push(item: T) {
+        this.lastPushed = item
+        return super.push(item)
+      }
+
+      indexOf(searchElement: T, fromIndex?: number | undefined): number {
+        this.lastSearched = searchElement
+        return super.indexOf(searchElement, fromIndex)
+      }
+    }
+
+    test('calls correct mutation method on Array subclass', () => {
+      const subArray = new SubArray(4, 5, 6)
+      const observed = reactive(subArray)
+
+      subArray.push(7)
+      expect(subArray.lastPushed).toBe(7)
+      observed.push(9)
+      expect(observed.lastPushed).toBe(9)
+    })
+
+    test('calls correct identity-sensitive method on Array subclass', () => {
+      const subArray = new SubArray(4, 5, 6)
+      const observed = reactive(subArray)
+      let index
+
+      index = subArray.indexOf(4)
+      expect(index).toBe(0)
+      expect(subArray.lastSearched).toBe(4)
+
+      index = observed.indexOf(6)
+      expect(index).toBe(2)
+      expect(observed.lastSearched).toBe(6)
+    })
+  })
 })