获取滚动条距离的几种问题

   //获取滚动条当前的位置 
        function getScrollTop() {
            var scrollTop = 0;
            if(document.documentElement && document.documentElement.scrollTop) {
                scrollTop = document.documentElement.scrollTop;
            } else if(document.body) {
                scrollTop = document.body.scrollTop;
            }
            return scrollTop;
        }

        //获取当前可视范围的高度 
        function getClientHeight() {
            var clientHeight = 0;
            if(document.body.clientHeight && document.documentElement.clientHeight) {
                clientHeight = Math.min(document.body.clientHeight, document.documentElement.clientHeight);
            } else {
                clientHeight = Math.max(document.body.clientHeight, document.documentElement.clientHeight);
            }
            return clientHeight;
        }

        //获取文档完整的高度 
        function getScrollHeight() {
            return Math.max(document.body.scrollHeight, document.documentElement.scrollHeight);
        }
        
        //滚动事件触发
        window.onscroll = function() {
            if(getScrollTop() + getClientHeight() == getScrollHeight()) {
               34             }
        }