let arr = [1, 2, [3, 4, 5, [6, 7], 8], 9, 10, [11, [12, 13]]]
const flatten = function (arr) {
while (arr.some(item => Array.isArray(item))) {
arr = [].concat(...arr)
}
return arr
}
console.log(flatten(arr))
原文：https://www.cnblogs.com/jaolo/p/11202585.html