我对对象数组的项使用了map方法，但此数组中的一个项也是对象的数组，因此我需要获取其属性

const mainArray = [
  { 
    id: 1, 
    name: 'John', 
    hobbies: [
      { hobby: 'reading', level: 'high' },
      { hobby: 'painting', level: 'medium' }
    ]
  },
  { 
    id: 2, 
    name: 'Jane', 
    hobbies: [
      { hobby: 'drawing', level: 'low' },
      { hobby: 'singing', level: 'high' }
    ]
  }
];

const hobbiesArray = mainArray.map(obj => obj.hobbies.map(item => item.hobby));

console.log(hobbiesArray);

[
  ['reading', 'painting'],
  ['drawing', 'singing']
]