JS数组reduce()方法详解及高级技巧

let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice'];
const recordTimes = names.reduce((prev, cur) => {
    if (cur in prev) {
        prev[cur]++
    } else {
        prev[cur] = 1
    }
    return prev
}, {})
console.log(recordTimes)

let arr = [1, 2, 3, 4, 4, 1]
const unique = arr.reduce((prev, cur) => {
    if(!prev.includes(cur)){
       return prev.concat(cur)
    }else{
        return prev
    }
}, [])
console.log(unique)

let arr = [[0, 1], [2, 3], [4, 5]]
const flatOne = arr.reduce((prev,cur)=>{
   return prev.concat(cur)
},[])
console.log(flatOne)

let arr = [[0, 1], [2, 3], [4, [5, 6, 7]], [2, 3, [2, 3, [2, 3, [2, [2, , [2, 3], 3], 3]]]]]
const flatten = arr => {
   return arr.reduce((prev, cur) => {
       return prev.concat(Array.isArray(cur) ? flatten(cur) : cur)
   }, [])
}
console.log(flatten(arr))

var result = [
  {
      subject: 'math',
      score: 10
  },
  {
      subject: 'chinese',
      score: 20
  },
  {
      subject: 'english',
      score: 30
  }
]
const totalSum = result.reduce((prev,cur)=>{
  return prev+cur.score
},0)
console.log(totalSum)