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));