observer:function(newVal){
   if(newVal){
     const author = util.getAuthor(newVal.author)
     this.setData({
       author
     })
     虽然可以这样写 但是 Bad
     const _book = Object.assign({}, this.properties.book,{
       author:util.getAuthor(newVal.author)
     })

     AirBnb推荐的写法
     const _book = {
       ...newVal,
       author:util.getAuthor(newVal.author)
     }
     this.setData({
       _book
     })

     这样做也是不行的 无法生效
     this.properties.book.author = util.getAuthor(newVal.author)
   }
 }