HarmonyOS ArkTS中怎么指定可变key值得对象？

typescript 
interface MyObject { 
  [key: string]: any; 
} 
 
const obj: MyObject = { 
  name: '小明', 
  age: 18, 
  gender: 'male' 
}; 
 
obj['hobby'] = ['reading', 'swimming'];