js数组整理成树形结构

 let arr = [
      { id: 1, name: '1', parentId: 0 },
      { id: 2, name: '2', parentId: 0 },
      { id: 3, name: '3', parentId: 0 },
      { id: 4, name: '1-1', parentId: 1 }
    ] 

方式一

 function arrToTree(arr, parentId = 0) {
      let newArr = []
      arr.forEach(item => {
        if (item.parentId === parentId) {
          newArr.push({
            ...item,
            children: arrToTree(arr, item.id)
          })
        }
      })
      return newArr
    }
  console.log(arrToTree(arr))

方式二

function arrToTree(arr,parentId = 0){
                return arr.filter(item => item.parentId === parentId).map(item => ({...item,children:arrToTree(arr,item.id)}))
        }
console.log(arrToTree(arr));

方式三

function arrayToTree(items) {
         const result = []; // 存放结果集
         const itemMap = {}; // 
         for (const item of items) {
             const id = item.id;
             const pid = item.parentId; 
               if (!itemMap[id]) {
                 itemMap[id] = {
                     children: [],
                 }
             } 
                itemMap[id] = {
                 ...item,
                 children: itemMap[id]['children']
             } 
            const treeItem = itemMap[id]; 
             if (pid === 0) {
                 result.push(treeItem);
             } else {
                 if (!itemMap[pid]) {
                     itemMap[pid] = {
                         children: [],
                     }
                 }
                 itemMap[pid].children.push(treeItem)
             }

         }
         return result;
     } 
 console.log(arrayToTree(arr));