数组打平

reduce

const arr = [1, [1, 2], 3, [[1, 2, 3], 4], 5]
const foo = function (arr) {
  return arr.reduce((total, curVal) => {
    total = total.concat(curVal instanceof Array ? foo(curVal) : curVal)
  }, [])
}
console.log(foo(arr))

flat

flat ES6 新增的数组拍平方法

const arr = [1, [1, 2], 3, [[1, 2, 3], 4], 5]
console.log(arr.flat(Infinity))

递归

const arr = [1, [1, 2], 3, [[1, 2, 3], 4], 5]
const foo = function (arr) {
  let temp = []
  for (let val of arr) {
    val instanceof Array ? temp.push(...foo(val)) : temp.push(val)
  }
  return temp
}
console.log(foo(arr))

toString

const arr = [1, [1, 2], 3, [[1, 2, 3], 4], 5]

console.log(arr.toString().split(',').map(item => Number(item)))

// [
//   1, 1, 2, 3, 1,
//   2, 3, 4, 5
// ]