问一个 ts 类型提取问题

interface Article {
  filename: string
  title: string
  date: string
}

const articles: Article[] = [
  {
    filename: 'article1',
    title: 'first article',
    date: '2021-04-13T18:10:40.578Z'
  },
  {
    filename: 'article2',
    title: 'second article',
    date: '2021-04-13T19:32:39.556Z'
  }
]

// 从 articles 的 filename 字段提取类型
// 结果 => type ArticleFilename = 'article1' | 'article2'
type ArticleFilename = ???