1. Js判断是否滚动到了底部
//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);
        }

        window.onscroll = function () {
            if (getScrollTop() + getClientHeight() == getScrollHeight()) {
                console.log("到达底部");
            }
        };