javascript - 如何从 Javascript 中的对象列表中获取不同的年份

Question

我在 Javascript 中有以下对象，我想从 createdOn 值返回不同年份的列表:

我试过以下但它返回一个空数组:

const things = [{
    "id": 1,
    "title": "First thing",
    "createdOn": "2017-12-07T15:44:50.123"
  },
  {
    "id": 2,
    "title": "Second thing",
    "createdOn": "2018-05-07T09:10:24.123"
  },
  {
    "id": 3,
    "title": "Third thing",
    "createdOn": "2018-12-07T12:07:50.123"
  },
  {
    "id": 4,
    "title": "Forth thing",
    "createdOn": "2018-12-07T16:39:29.123"
  }
]

console.log(things.map(thing => new Date(thing.createdOn).getFullYear()).filter((value, index, self) => self.indexOf(value) === index))

我在这里错过了什么？

非常感谢。

Answer 1

您在 .map() 的回调中使用了拼写错误的参数，即将 thing 替换为 event。您还可以使用 Set 来获取唯一值:

const data = [
  {"id": 1, "title": "First thing", "createdOn": "2017-12-07T15:44:50.123"}, 
  {"id": 2, "title": "Second thing", "createdOn": "2018-05-07T09:10:24.123"}, 
  {"id": 3, "title": "Third thing", "createdOn": "2018-12-07T12:07:50.123"}, 
  {"id": 4, "title": "Forth thing", "createdOn": "2018-12-07T16:39:29.123"}
];

const result = [...new Set(data.map(event => new Date(event.createdOn).getFullYear()))];

console.log(result);