学习目标：练习常用数组api

题目1

[“b”, “c”,“b”, “c”,“a”, “b”, “c”] 统计每个元素出现的次数,结果是： {a：1，b: 3, c: 3}

let arr = ["b", "c","b", "c","a", "b", "c"] 
// 你的代码 ...
let obj = arr.reduce(function(prev,cur){
  if( cur in prev){
    prev[cur]++
  }else{
    prev[cur] = 1
  }
  return prev
},{})
console.log(obj) // ==> {a：1， b: 3, c:  3}

题目2

[{ label: ‘男’, value: 1 }, { label: ‘女’, value: 0 }] 转为 {‘1’: ‘男’, ‘0’: ‘女’}

var arr = [{ label: '男', value: 1 }, { label: '女', value: 0 }]

let obj = arr.reduce((prev,cur) =>{
  prev[cur.value] = cur.label
  return prev
},{})

console.log(obj) //  {'1': '男',  '0': '女'}