js 数组转树方法

##方法1
function array2Tree(array) {
    const result = []
      if (!Array.isArray(array)) {
        return result
      }
      array.forEach(item => {
        delete item.children
      })
      const map = {}
      array.forEach(item => {
        map[item.id] = item
      })
      array.forEach(item => {
        const parent = map[item.parentId]
        if (parent) {
          (parent.children || (parent.children = [])).push(item)
        } else {
          result.push(item)
        }
      })
      return result
    }
##方法2
/**
*通过递归实现
* data 数组数据
* pid 顶级元素的parentId值
*/
function array2Tree (data, pid) {
  let result = []
  let temp
  for (let i = 0; i < data.length; i++) {
    if (data[i].parentId === pid) {
      let obj = {id: data[i].id, name: data[i].name}
      temp = array2Tree(data, data[i].id)
      if (temp.length > 0) {
        obj.children = temp
      }
      result.push(obj)
    }
  }
  return result
}

const array = [
    {id:1, parentId: null, name: 'a'},
    {id:2, parentId: null, name: 'b'},
    {id:3, parentId: 1, name: 'c'},
    {id:4, parentId: 2, name: 'd'},
    {id:5, parentId: 1, name: 'e'},
    {id:6, parentId: 3, name: 'f'},
]
arrayToTree(array)