本文实例讲述了JS实现先显示大图后自动收起显示小图的广告代码。分享给大家供大家参考。具体如下：
这是一个非常不错的JavaScript图片特效，当最初打开网页的时候，显示的是大图片，就像遮屏广告一样，停留一会后，自动缓慢收起，这时由JS控制更换广告图片，始终显示在网页顶部，在一些大门户网站我们经常见到这种效果，个人感觉挺酷哦！
先来看看运行效果截图：
在线演示地址如下：
http://demo.jb51.net/js/2015/js-big-to-small-pic-adv-codes/
具体代码如下：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN""http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>先显示大图随后自动收起显示小图的JS广告</title><meta http-equiv="content-type" content="text/html;charset=gb2312"><style type="text/css">html,body{margin:0;text-align:center;font-size:12px;}img{border:none}p{margin:0px}</style><script type="text/javascript">var showAD = {curve: function(t, b, c, d, s) {if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;return c / 2 * ((t -= 2) * t * t + 2) + b},fx: function(from, to, playTime, onEnd) {var Me = this,who = this.adWrap,position = 0,changeVal = to - from,curve = this.curve;playTime = playTime / 10;who.style.overflow = 'hidden';function _run() {if (position++<playTime) {who.style.height = Math.max(1, Math.abs(Math.ceil(curve(position, from, changeVal, playTime)))) + "px";setTimeout(_run, 10)} else {onEnd && onEnd.call(Me, to)}};_run()},init: function(info) {var Me = this,loadImg = new Image;loadImg.src = info.endImgURL;window.onload=function() {Me.endImgURL = info.endImgURL;Me.img = document.getElementById(info.imgID);Me.adWrap = document.getElementById(info.adWrapID);var max = Me.img.height;setTimeout(function() {Me.fx(max, 0, 500,function(x) {this.img.src = this.endImgURL;this.curve = function(t, b, c, d) {if ((t /= d) < (1 / 2.75)) {return c * (7.5625 * t * t) + b} else if (t < (2 / 2.75)) {return c * (7.5625 * (t -= (1.5 / 2.75)) * t + .75) + b} else if (t < (2.5 / 2.75)) {return c * (7.5625 * (t -= (2.25 / 2.75)) * t + .9375) + b} else {return c * (7.5625 * (t -= (2.625 / 2.75)) * t + .984375) + b}};this.fx(0, this.img.height,600)})},info.timeout || 1000)};}};showAD.init({adWrapID: 'ad_box_2009_06',imgID: 'adImg',endImgURL: 'images/as.jpg'});</script></head><body><div id="ad_box_2009_06"><img src="images/ab.jpg" id="adImg"></div></body></html>希望本文所述对大家的javascript程序设计有所帮助。
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