JavaScript 多维数组转一维数组

Question

最新的 ES 规范其实也加入了这个方法，功能是将一个数组压平，比如 [1, 2, [3, [4, 5, [6, [7, 8]]]]]，会被处理成 [1, 2, 3, 4, 5, 6, 7, 8]。更进一步，实现可以压平指定深度的数组。

function flatten(list) {
  if (list.length === 0) return [];
  const head = list[0];
  if (head instanceof Array) {
    list[0] = flatten(head);
  } else {
    list[0] = [list[0]];
  }
  return list[0].concat(flatten(list.slice(1)));
}

function flattenDepth(list, n) {
  if (list.length === 0) return [];
  if (n === 0) return list;
  const head = list[0];
  if (head instanceof Array) {
    list[0] = flattenDepth(head, n - 1);
  } else {
    list[0] = [list[0]];
  }
  return list[0].concat(flattenDepth(list.slice(1), n));
}

// test
const a = flatten([1, 2, [3, [4, 5, [6, [7, 8]]]]]);
console.log(a);

const b = flattenDepth([1, 2, [3, [4, 5, [6, [7, 8]]]]], 2);
console.log(b);

const c = flattenDepth([1, 2, [3, [4, 5, [6, [7, 8]]]]], Number.MAX_VALUE);
console.log(c);