将滚动条置顶,置底

Message.prototype.setScrollToBottom = function () {
    // 整个文档所占的高度
    var scrollHeight = (function getScrollHeight(){
        var scrollHeight = 0, bodyScrollHeight = 0, documentScrollHeight = 0;
        if(document.body){
            bodyScrollHeight = document.body.scrollHeight;  
        }
        if(document.documentElement){
            documentScrollHeight = document.documentElement.scrollHeight;
        }
        scrollHeight = (bodyScrollHeight - documentScrollHeight > 0) ? bodyScrollHeight : documentScrollHeight;
        return scrollHeight;
    })();
    //可见区域的高度
    var windowHeight = (function getWindowHeight(){
        if(document.documentElement.clientHeight){
            return document.documentElement.clientHeight;  
        } else {
            return document.body.clientHeight;
        }
    })();
    document.body.scrollTop = scrollHeight - windowHeight;
    document.documentElement.scrollTop = scrollHeight - windowHeight;  // 页面置底

　　document.body.scrollTop = 0；//页面置顶
　　document.documentElement.scrollTop = 0；
};