JS 版
<!DOCTYPE html><html><head> ???<style type="text/css"> ???????#showIt { ???????????width: 200px; ???????????height: 200px; ???????????background-color: red; ???????????position: absolute; ???????????top: 1500px; ???????} ???</style></head><body style="height:2000px;"> ???<div id="showIt"></div></body><script type="text/javascript"> ???document.onscroll = function() { ???????var scrollTop = document.documentElement.scrollTop || document.body.scrollTop; ???????var cHeight = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight; ???????var oDiv = document.getElementById(‘showIt‘); ???????if (scrollTop > (oDiv.offsetTop - cHeight)) ???????????alert(‘触发了‘) ???}</script></html>JQ版
$(document).scroll(function() { ???sTop = $(this).scrollTop(); //获取滚动条的位置 ???var sh = $(window).height();//视口高度 ???var ft = $("footer").offset().top//指定元素距离文档顶部高度 ???????// 滚动条位置 大于 指定元素减去 视口高度时 ???if (sTop > (ft - sh)) { //当底部出现在视口时 触发 ???????//dododo ???}}JS 滚动条滚动到指定元素触发
原文地址：http://www.cnblogs.com/xzma/p/7698668.html