平级数据转树形结构

// 自动寻找顶级节点
function getTree(items) {
  var ids = items.map(e => e.id);
  let pids = items.filter(e => !ids.includes(e.pid));
  let index = 0;
  return pids.map(e => {
    e.level = index;
    e.children = handler(items, e.id, index + 1);
    return e
  });
}
// 返回指定pid节点的子级
function handler(items, pid, index) {
  var _arr = [];
  items.forEach(item => {
    if (pid === item.pid) {
      item.level = index + 1;
      let arr = handler(items, item.id, index + 1);
      if (arr.length) item.children = arr;
      _arr.push(item);
    }
  });
  return _arr;
}