HarmonyOS json的解析问题

@Entry 
@Component 
struct Index { 
  @State message: string = 'Hello World'; 
  build() { 
    Row() { 
      Column() { 
        Button(this.message) 
          .fontSize(50) 
          .fontWeight(FontWeight.Bold) 
          .onClick(() => { 
            let a = new A() 
            let b = new B() 
            b.name = 'ni hao' 
            a.b = b 
            let json = JSON.stringify(a) 
            console.log(json) 
            let temp = JSON.stringify(json) as A 
            //为什么这里输出是false 
            console.log("why not :" + (temp instanceof A)) 
          }) 
      } 
      .width('100%') 
    } 
    .height('100%') 
  } 
} 
class A { 
  b?: B 
  bb?: string 
} 
class B { 
  name ?: string 
}