点击回到顶部

<script>
    /*
    * 固定时间回到顶部
    * */
    var btn = document.getElementById('btn');

    btn.onclick = function () {
        // clearInterval(this.timer);
        if(this.running)return;
        this.running = true;
        var duration = 1000;
        var changeL = utils.scrollT();// 当前页面卷上去的高度
        var speed = changeL/duration;
        this.timer = window.setInterval(() => {
            var moveL = speed*30;
            changeL = utils.scrollT();
            if(changeL <= 0){
                clearInterval(this.timer);
                this.running = false;
            }
            document.documentElement.scrollTop -= moveL;
            document.body.scrollTop -= moveL;
        },30)
    };
    function btnDis() {
        var scrT = utils.scrollT();
        if(scrT > 400){
            btn.style.display = 'block';
        }else {
            btn.style.display = 'none';
        }
    };
    window.onscroll = function () {
        btnDis();
    };
    window.onmousewheel = function () {
        clearInterval(btn.timer);
        btn.running = false;
    }
</script>