关于Array中reduce的实际应用

  // 数组中所有值求和
    let arr = [0, 1, 2, 3]
    let sum = arr.reduce((accumulator, currentValue)=> {
      return accumulator + currentValue;
    }, 0);
    console.log(sum) 

  // 二位数组转化为一维数组
  let array2 = [[0, 1], [2, 3], [4, 5]]
  let array = array2.reduce((first, last) => {
    return first.concat(last)
  }, [])
  console.log(array)

  //计算数组中每个元素出现的次数
  let names = ['hbh', 'zz', 'yd', 'wan', 'hbh', 'hbh', 'wan', 'zz']
  let obj = {}
  names.reduce((before, after) => {
    before[after] ? before[after]++ : before[after] = 1
    return before
  }, obj)
  console.log(obj)

  // 根据属性对object进行分类
  let people = [
    {name: 'Alice', age: 21},
    {name: 'Max', age: 20},
    {name: 'Jane', age: 20}
  ]
  let group = {}
  people.reduce(((before, after) => {
    before[after.age] ? before[after.age].push(after) : before[after.age] = [after]
     return before
  }), group)
    console.log(group)

上述内容源自mdn中reduce中例子，https://developer.mozilla.org/zh-CN/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce