vue 中判斷向上滾動還是向下滾動

 <script>
    export default {
        data(){
            return{
                       i = 0
               }
           },
       mounted () {
            window.addEventListener('scroll', this.handleScroll, true);  
             // 監聽（綁定）滾輪 滾動事件
        },
        methods:{
         handleScroll(){
            // 頁面滾動距頂部距離
            var scrollTop = window.pageYOffset || document.documentElement.scrollTop || 
                      document.body.scrollTop
            var scroll = scrollTop - this.i;
            this.i = scrollTop;
            if(scroll<0){
                console.log('up')
            }else{
                console.log('down')
            }
        },
}