因为它是一个对象，我们不能访问它的键“Home Work”作为索引0，但你可以尝试Object.keys（yourObject）访问它的所有键.

只需使用Object.keys()方法就可以得到对象的键的索引号，该方法返回对象的所有键的列表，然后使用forEach方法遍历键列表，得到每个键的索引。

• • 示例：**

var yourObject = {
"Home work": [
    {
        "id": 5,
        "student_id": 2,
        "activity_id": 3,
        "checked": 1,
        "checked_at": "2023-02-07 06:03:06",
        "completed": 1,
        "created_at": "2023-02-06T12:31:22.000000Z",
        "updated_at": "2023-02-07T06:03:11.000000Z",
        "activity_category_name": "Home work"
    },
    {
        "id": 2,
        "student_id": 2,
        "activity_id": 2,
        "checked": 1,
        "checked_at": "2023-02-07 06:03:38",
        "completed": 0,
        "created_at": "2023-02-06T10:44:31.000000Z",
        "updated_at": "2023-02-07T06:03:38.000000Z",
        "activity_category_name": "Home work"
    }
],
"Daily activity": [
    {
        "id": 1,
        "student_id": 2,
        "activity_id": 1,
        "checked": 1,
        "checked_at": "2023-02-05 11:18:56",
        "completed": 1,
        "created_at": "2023-02-05T10:40:25.000000Z",
        "updated_at": "2023-02-05T11:18:56.000000Z",
        "activity_category_name": "Daily activity"
    }
]}

要同时获取键及其索引，请使用：

Object.keys(yourObject ).forEach((key, index) => {
    console.log(`Key:: ${key}, index:: ${index}`)
})

如果只想获取键的索引，请使用：

Object.keys(yourObject ).forEach((key, index) => {
    console.log(index)
})

试试这个代码

var json = {
      "Home work": [
        {
          "id": 5,
          "student_id": 2,
          "activity_id": 3,
          "checked": 1,
          "checked_at": "2023-02-07 06:03:06",
          "completed": 1,
          "created_at": "2023-02-06T12:31:22.000000Z",
          "updated_at": "2023-02-07T06:03:11.000000Z",
          "activity_category_name": "Home work"
        },
        {
          "id": 2,
          "student_id": 2,
          "activity_id": 2,
          "checked": 1,
          "checked_at": "2023-02-07 06:03:38",
          "completed": 0,
          "created_at": "2023-02-06T10:44:31.000000Z",
          "updated_at": "2023-02-07T06:03:38.000000Z",
          "activity_category_name": "Home work"
        }
      ],
      "Daily activity": [
        {
          "id": 1,
          "student_id": 2,
          "activity_id": 1,
          "checked": 1,
          "checked_at": "2023-02-05 11:18:56",
          "completed": 1,
          "created_at": "2023-02-05T10:40:25.000000Z",
          "updated_at": "2023-02-05T11:18:56.000000Z",
          "activity_category_name": "Daily activity"
        }
      ]
    };

    var keys = Object.keys(json);
    for (const key of keys) {

      console.log(key);
      var result = keys.indexOf(key);
      console.log(result);
    }