关键词：JS数组降维、reduce数组降维
原生Array.prototype.flat方法接受一个depth参数，默认值为1，depth表示要降维的维数：
输出结果：
const arr = [1, [2, 3], [4, [5, 6]]]
console.log(arr.flat(1)) // [1, 2, 3, 4, [5, 6]]
console.log(arr.flat(Infinity)) // [1, 2, 3, 4, 5, 6]reduce + 递归实现方案
// MDN: 可查看更多flat实现方法
function flat(arr = [], depth = 1) {
if (arr.length === 0) {
return []
}
let result = []
if (depth > 0) {
result = arr.reduce((acc, val) => {
return acc.concat(Array.isArray(val) ? flat(val, depth - 1) : val)
}, [])
} else {
result = arr.slice()
}
return result
}
const arr = [1, 2, 3, [1, 2, 3, 4, [2, 3, 4]]]
const myResult1 = flat(arr, 1)
const originResult1 = arr.flat(1)
const myResult2 = flat(arr, Infinity)
const originResult2 = arr.flat(Infinity)
console.log(myResult1) // [1, 2, 3, 1, 2, 3, 4, [2, 3, 4]]
console.log(originResult1) // [1, 2, 3, 1, 2, 3, 4, [2, 3, 4]]
console.log(myResult2) // [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]
console.log(originResult2) // [1, 2, 3, 1, 2, 3, 4, 2, 3, 4]