配合下拉刷新、上拉加载的返回顶部demo（适用任何页面）

看到很多人提到了这个问题，正好自己也需要返回顶部的操作，总结了下各处的问题与回答，把实现的代码放出来，供参考。

下拉刷新、上拉加载的容器和返回顶部按钮，按钮默认不显示：

<div id="pullrefresh" class="mui-scroll-wrapper">  
    <div class="mui-scroll">  
        <ul id="list" class="mui-table-view"></ul>  
    </div>  
</div>  

<a id="scrollToTop" class="backTop hide">  
    <span class="mui-icon mui-icon-arrowup"></span>  
</a>

按钮对应的css：

.hide {  
    display: none;  
}  
.backTop {  
    background: #DDDDDD;  
    border-radius: 50%;  
    position: fixed;  
    right: 10px;  
    bottom: 15px;  
    width: 38px;  
    height: 38px;  
    z-index: 9999;  
    text-align: center;  
    font-size: 18px;  
    color: #666666;  
    padding-top: 8px;  
    opacity: 0.8;  
}

js中添加事件监听：

var scrollToTopBox = document.getElementById('scrollToTop');  
//返回按钮tap  
scrollToTopBox.addEventListener('tap', function(e) {  
    e.stopPropagation();  
    mui('#pullrefresh').pullRefresh().scrollTo(0, 0, 100);//滚动到顶部  
});  
//Android上监听原生滚动，iOS上监听div滚动，上拉超过一屏后显示按钮，否则隐藏，可自行在条件判断中修改  
if (mui.os.android) {  
    window.addEventListener('scroll', function(e) {  
        if (window.pageYOffset >= window.innerHeight && scrollToTopBox.classList.contains('hide'))  
            scrollToTopBox.classList.remove('hide');  
        else if (window.pageYOffset < window.innerHeight && !scrollToTopBox.classList.contains('hide'))  
            scrollToTopBox.classList.add('hide');  
    });  
} else {  
    document.getElementById('pullrefresh').addEventListener('scroll', function() {  
            if (mui('#pullrefresh').pullRefresh().y <= window.innerHeight * (-1) && scrollToTopBox.classList.contains('hide'))  
                scrollToTopBox.classList.remove('hide');  
            else if (mui('#pullrefresh').pullRefresh().y > window.innerHeight * (-1) && !scrollToTopBox.classList.contains('hide'))  
                scrollToTopBox.classList.add('hide');  
    });  
}

该方法也可用于任何需要返回顶部的页面，做一下适当的修改，此时不区分Android和iOS，代码如下：

var scrollToTopBox = document.getElementById('scrollToTop');  
        scrollToTopBox.addEventListener('tap', function(e) {  
            e.stopPropagation();  
            mui('body').pullRefresh().scrollTo(0, 0, 100);  
        });  
        window.addEventListener('scroll', function() {  
            if (window.pageYOffset >= window.innerHeight && scrollToTopBox.classList.contains('hide'))  
                scrollToTopBox.classList.remove('hide');  
            else if (window.pageYOffset < window.innerHeight && !scrollToTopBox.classList.contains('hide'))  
                scrollToTopBox.classList.add('hide');  
        });