JS与PHP递归的区别

<?php
$areas=[
    ['id'=>1,'pid'=>0,'name'=>'中国'],
    ['id'=>2,'pid'=>1,'name'=>'山东省'],
    ['id'=>3,'pid'=>1,'name'=>'北京市'],
    ['id'=>4,'pid'=>2,'name'=>'济南市'],
    ['id'=>5,'pid'=>4,'name'=>'历下区'],
    ['id'=>6,'pid'=>2,'name'=>'临沂市'],
    ['id'=>7,'pid'=>6,'name'=>'郯城县'],
    ['id'=>8,'pid'=>6,'name'=>'沂水县'],
];

function tree($id,&$item){
    global $areas;
    foreach ($areas as $area){
        if(!isset($area['child'])){
            $area['child']=[];
        }
        if($area['pid']==$id){
            $item[]=$area;
            tree($area['id'],$item[count($item)-1]['child']);
            if(empty($item[count($item)-1]['child'])){
                unset($item[count($item)-1]['child']);
            }
        }
    }
}
tree(0,$items);

<script>
    let areas=<?php echo json_encode($areas)?>;
    function tree(pid,$items){
        areas.forEach(item => {
            if (pid === item.pid) {
                let child = {
                    value: item.id,
                    label: item.name,
                    children: [],
                }
                $items.push(child)
                this.tree(item.id, child.children)
                if (child.children.length === 0) {
                    delete child.children
                }
            }
        })
    }
    let items=[]
    tree(0,items)
    console.log(items)
</script>

今天想用js的方式写个递归，后来就是不行。。。。
看来是有差别的。。。。。