Object.assignエラー

flow.js

/* @flow */
type Article = {
  id: string
}

type State = {
  articles: Article[]
}

const state: State = {
  articles: [{ id: 'fuga' }]
}
const newArticle = [
  {
    id: 'hoge'
  }
]
const article: Article[] = Object.assign([], state.articles, newArticle)
console.log(article)
// 31: const article: Array<Article> = Object.assign({}, state.articles, newArticle)
//                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ call of method `assign`. Expected object instead of
// 31: const article: Array<Article> = Object.assign({}, state.articles, newArticle)
//                                                       ^^^^^^^^^^^^^^ array type

hoge.ts

interface Article {
  id: string
}

interface State {
  articles: Article[]
}

const state: State = {
  articles: [{ id: 'fuga' }]
}
const newArticle = [
  {
    id: 'hoge'
  }
]
const article: Article[] = Object.assign({}, state.articles, newArticle)
console.log(article)
// {"0":{"id":"hoge"}}