当我激活变更事件时,如何获取与下拉列表对应的JSON?

我怎样才能完全得到JSON?例如,如果我选择第二个选项,我希望获得:

{"name":"goku", "ki":23232, "planet":"vegita"}

这是我的代码:

 <select  [(ngModel)]="dropdown" (change)="fn_change(item)">
   <option *ngFor="let item of aData" value="item.name">{{item.name}} 
   </option>
 </select>

aData=[
 {"name":"goku", "ki":23232, "planet":"vegita"},
 {"name":"vegeta", "ki":11, "planet":"vegita"},
 {"name":"krillin", "ki":5565, "planet":"earth"}        
]

 fn_change(item){
  alert(item);
  console.log(item);
}

我该怎么做?

https://stackblitz.com/edit/angular-y6crza?file=src/app/app.component.ts