[JavaScript知识库]reduce处理数组成多层子级新数组

let arr = [
      {
        id:1,
        name:'er',
        pid:0
      },
      {
        id:2,
        name:'we',
        pid:1,
      },
      {
        id:3,
        name:'ert',
        pid:2,
      },
    ]
 //处理成
 let arr02 = [
 	 {
        id:1,
        name:'er',
        pid:0,
        child:[
        	  {
		        id:2,
		        name:'we',
		        pid:1,
		        child:[
		        	 {
			        id:3,
			        name:'ert',
			        pid:2,
			      }
				]
		   }
        ]
      },
]
//注明：这个封装函数处理的方法是一个掘金评论区大佬写的
function arrBoth(arr){
	let req = arr.reduce((prev,next)=>{
		let parent = arr.find(item=>item.id === next.pid);
		if(parent){
			parent.child || =[];//这个用法晓得的可以说下，谢谢
			parent.child.push(next);
		}else{
			prev.push(next)
		}
		return prev;
	},[])
	return req;
}
console.log(arrBoth(arr));