模拟实现数组扁平化

function flat(list) {
  const traverse = (target, depth) => {
    const result = [];

    for (let ele of target) {
      if (Array.isArray(ele)) {
        result = result.concat(traverse(ele, depth));
      } else {
        result.push(ele);
      }
    }

    return result;
  };

  return traverse(list);
}