⭐⭐⭐Steamroller-扁平化数组

freeCodeCamp.org

Steamroller

Flatten a nested array. You must account for varying levels of nesting.

答案

freeCodeCamp Challenge Guide: Steamroller

关于展开运算符

关键点在于初始化传入第二个参数空数组用来记录

function steamrollArray(arr, res = []) {
  arr.forEach(x => {
    if (Array.isArray(x)) {
      steamrollArray(x, res)
    } else {
      res.push(x)
    }
  })
  return res
}
console.log(
  steamrollArray([1, [2], [3, [[4]]]])
)