js返回树形结构数据

/**
 * 树形结构转换
 * @param a
 * @param idStr
 * @param pidStr
 * @param chindrenStr
 * @returns {Array}
 */
function transData(a, idStr, pidStr, chindrenStr){
    let r = [], hash = {}, id = idStr, pid = pidStr, children = chindrenStr, i = , j = , len = a.length;
    for(; i < len; i++){
        hash[a[i][id]] = a[i];
    }
    for(; j < len; j++){
        let aVal = a[j], hashVP = hash[aVal[pid]];      //当前对象&pid对象
        if(hashVP){
            !hashVP[children] && (hashVP[children] = []);
            hashVP[children].push(aVal);
        }else{
            r.push(aVal);
        }
    }
    return r;
}

/**
 * 树形结构转换
 * @param a
 * @param idStr
 * @param pidStr
 * @returns {Array}
 */
function transData2Tree(a, idStr, pidStr) {
  var r = []
  var hash = {}
  var len = a.length
  for (var i = 0; i < len; i++) {
    hash[a[i][idStr]] = a[i]
  }
  for (var j = 0; j < len; j++) {
    var aVal = a[j]
    var hashVP = hash[aVal[pidStr]]
    if (hashVP) {
      (!hashVP.children) && (hashVP.children = [])
      hashVP.children.push(aVal)
    } else {
      r.push(aVal)
    }
  }
  return r
}

/**
 * 返回一个节点下的所有子孙节点
 */
function getChildren(arr, result, pid) {
  for (var i in result) {
    if (result[i].pid + '' === pid + '') {
      arr.push(result[i]._id + '')
      getChildren(arr, result, result[i]._id)
    }
  }
  return arr
}