function addScrollEvent() {        let canScroll = true;        function isScrollToPageBottom() {            let docHeight = document.documentElement.offsetHeight;            let viewHeight = window.innerHeight;            let scrollHeight = window.pageYOffset;            return docHeight - viewHeight - scrollHeight < 20;        }        document.onscroll = function () {            // console.log(isScrollToPageBottom());// true 为底部            if (canScroll && isScrollToPageBottom()) {
   // 滑到底部                canScroll = false;                if (arr.length > 5) {                    document.getElementsByClassName('content')[0].innerHTML = '1000'; // 处理一些事件                }                else {                    canScroll = true;                }            }        }.bind(this);    }