1. 找出是否有人超过 19 岁？

 const people = [
      { name: 'Wes', year: 1988 },
      { name: 'Kait', year: 1986 },
      { name: 'Irv', year: 1970 },
      { name: 'Lux', year: 2015 }
 ]
function some(arr){
   return arr.some(item => (new Date().getFullYear() - item.year) >= 19)
}

2.是否所有人都是成年人

 const people = [
      { name: 'Wes', year: 1988 },
      { name: 'Kait', year: 1986 },
      { name: 'Irv', year: 1970 },
      { name: 'Lux', year: 2015 }
 ]
function every(arr) {
    return arr.every(item =>  (new Date().getFullYear() - item.year) >= 18)
}

3.找到 ID 号为 823423 的评论

const comments = [
      { text: 'Love this!', id: 523423 },
      { text: 'Super good', id: 823423 },
      { text: 'You are the best', id: 2039842 },
      { text: 'Ramen is my fav food ever', id: 123523 },
      { text: 'Nice Nice Nice!', id: 542328 }
 ];
function find(arr){
  return arr.find(item => item.id ===823423 )
}

4.删除 ID 号为 823423 的评论

const comments = [
      { text: 'Love this!', id: 523423 },
      { text: 'Super good', id: 823423 },
      { text: 'You are the best', id: 2039842 },
      { text: 'Ramen is my fav food ever', id: 123523 },
      { text: 'Nice Nice Nice!', id: 542328 }
 ];
function findIndex(arr){
   return arr.findIndex(item => item.id ===823423)
}
const index = findIndex(comments)
comments.splice(index,1)

5.把数组的对象元素的某一项拼接成字符串

const goodImgs = [
  {url: 'www.hcc.com'},
  {url: 'www.yx.com'}
]
var strImages = goodImgs.reduce((str,item)=>{
  return  str+`![](${item.url})`
},'')

6.完成下列数组的常用操作

问题

 let todos = [
  {
    id: 1001,
    title: '请找出这个数组中第一个id为1005的todo的位置',
    completed: false
  },
  {
    id: 1002,
    title: '请找出这个数组中所有completed为true的todo',
    completed: true
  },
  {
    id: 1005,
    title: '这个数组中todo的completed都是true吗',
    completed: false
  },
  {
    id: 1004,
    title: '给所有todo的id加10',
    completed: true
  },
  {
    id: 1003,
    title: '计算所有todo的id的和',
    completed: false
  }
] 

答案

todos.findIndex((todo) => {
  return todo.id === 1005
})

todos.filter((todo) => {
  return todo.completed
})

todos.every((todo) => {
  return todo.completed
})

todos.map((todo) => {
  todo.id+=10
  return todo
})

todos.reduce((total,todo) => {
  return total+todo.id;
},0)