我们经常会遇到想处理扁平化数据，例如数据是这样的：

var json = '{"code":0,"parent":[{"name":"文件夹1","pid":0,"id":1},{"name":"文件夹2","pid":0,"id":2},{"name":"文件夹3","pid":0,"id":3},{"name":"文件夹1-1","pid":1,"id":4},{"name":"文件夹2-1","pid":2,"id":5}],"child":[{"name":"文件1","pid":1,"id":10001},{"name":"文件2","pid":1,"id":10002},{"name":"文件2-1","pid":2,"id":10003},{"name":"文件2-2","pid":2,"id":10004},{"name":"文件1-1-1","pid":4,"id":10005},{"name":"文件2-1-1","pid":5,"id":10006}]}';   

目前测试过有效的方法有两种方法
第一种：（采用两层fiter）

    data = JSON.parse(json);
    var result = transformData(data);
    console.log(result);
    function transformData(data) {
        let allData = JSON.parse(JSON.stringify(data));
        var data_new = [...allData.parent,...allData.child];
        console.log(data_new);
    　　 var result = data_new.filter(parent=>{
    　　　　let findChildren = data_new.filter(child=>{
    　　　　　　return parent.id === child.pid
    　　　　})
            if(findChildren.length>0)  parent.children = findChildren;
    // 　　　　findChildren.length>0 ? parent.children = findChildren : parent.children = []
    　　　　return parent.pid == 0   //返回顶层，依据实际情况判断这里的返回值
    　　 })
        return result;
    }

第二种：（采用reduce）

function transformData(data) {
     let allData = JSON.parse(JSON.stringify(data));
     var data_new = [...allData.parent,...allData.child];
     let treeMapList = data_new.reduce((obj, current) => {
         current.label = current.label || current.name;
         obj[current["id"]] = current;
         return obj;
     }, {});
     //看每个对象中pid值是否跟treeMapList中id的值相等，若相等就说是children中的数据
     let result = data_new.reduce((arr, current) => {
         let pid = current.pid;
         let parent = treeMapList[pid]; //拿父亲的数据
         if (parent) {
         parent.children
             ? parent.children.push(current)
             : (parent.children = [current]);
         } else if (pid === 0) {
         arr.push(current);
         }
         return arr;
     }, []);
     return result;
 }