程序源码复制代码代码如下:var floatAd = {};floatAd.getScrollTop = function(node) {var doc = node ? node.ownerDocument : document;return doc.documentElement.scrollTop || doc.body.scrollTop;};floatAd.getScrollLeft = function(node) {var doc = node ? node.ownerDocument : document;return doc.documentElement.scrollLeft || doc.body.scrollLeft;};floatAd.getBrowser = function() {var d = document.documentElement;return {width: window.innerWidth || (d && d.clientWidth) || document.body.clientWidth,height: window.innerHeight || (d && d.clientHeight) || document.body.clientHeight}};floatAd.extend = function(destination, source) {for(var property in source) {destination[property] = source[property];}return destination;};/* 默认属性扩展 */ floatAd.setOptions = function(options) {this.options = {delay: 20, // 调整速率fadeTime: 1 // 自动消失时间};return this.extend(this.options, options || {});};/* 类初始化 */ floatAd.init = function(id, options) {var _this = this;this.extend(this, this.setOptions(options));this.control = document.getElementById(id);var _callback = function() { // fadeIn完成后的回调函数_this.timer = window.setInterval(function() { _this.scroll() }, _this.delay); // 滚动定位window.setTimeout(function() { _this.fadeOut() }, _this.fadeTime * 1000); // 在固定时间内消失}this.fadeIn(_callback);window.onresize = function() { _this.setCenter(); }};/* 定时滚动 */ floatAd.scroll = function() {this.start = parseInt(this.control.style.top, 10);this.end = parseInt(this.getScrollTop() + this.getBrowser().height - this.control.clientHeight, 10);if(this.start != this.end) {this.amount = Math.ceil(Math.abs(this.end - this.start) / 15); /* 递减公式(this.start无限增大,整个分子无限减小,整个值就无限趋近于0) */ this.control.style.top = parseInt(this.control.style.top, 10) + ((this.end }};/* 目标居中并处于最底部 */ floatAd.setCenter = function() {this.top = this.getScrollTop() + floatAd.getBrowser().height;this.left = (this.getScrollLeft() + floatAd.getBrowser().width - this.control.clientWidth) / 2;this.control.style.top = this.top + 'px';this.control.style.left = this.left + 'px';};/* fadeIn */ floatAd.fadeIn = function(callback) {var _this = this, _top = 0;this.control.style.display = 'block'; // *要提前显示.不然无法取得clientWidth this.setCenter();var _timer = window.setInterval(function() {_this.control.style.top = _this.getScrollTop() + _this.getBrowser().height - (++_top) + 'px';if(_top >= _this.control.clientHeight) {window.clearInterval(_timer);callback && callback();}}, 2);};/* fadeOut */ floatAd.fadeOut = function() {var _this = this, _num = 0, _top = _this.control.clientHeight;window.clearTimeout(this.timer);var _timer = window.setInterval(function() {if(_top window.clearInterval(_timer);_this.control.style.display = 'none';} else {_this.control.style.top = _this.getScrollTop() + _this.getBrowser().height - (--_top) + 'px';}}, 2);this.control.style.top = (parseInt(this.control.style.top, 10) + 100) + 'px';};var newAd = 'start';document.getElementById('show').onclick = function() {if(newAd == 'start') {newAd = floatAd.init('ad', { fadeTime: 10 });}}程序原理整个广告运行具有四步动作.
1. 初始化时隐藏于页面最底部.
2. 自底向上升起.直到整个广告漂浮出来
3. 启动检测.滚动时保持广告始终处于页面中间最底部.
4. 到达自定义间隔时间.广告自动渐隐.
整个实现最重要的就是控制广告距离文档(非窗口)最顶部的距离.(scrollTop + browser.clientHeight).这里提供了获取这几个值的代码.
获取scrollTop, scrollLeft注意Chrome和Safari即使在标准doc模式下的根文档也是document.body而不是document.documentElement复制代码代码如下:floatAd.getScrollTop = function(node) {var doc = node ? node.ownerDocument : document;return doc.documentElement.scrollTop || doc.body.scrollTop;};floatAd.getScrollLeft = function(node) {var doc = node ? node.ownerDocument : document;return doc.documentElement.scrollLeft || doc.body.scrollLeft;};获取可视窗口的宽高复制代码代码如下:floatAd.getBrowser = function() {var d = document.documentElement;return {width: window.innerWidth || (d && d.clientWidth) || document.body.clientWidth,height: window.innerHeight || (d && d.clientHeight) || document.body.clientHeight}};代码思路流程初始化(init) -----> 设置居中并隐藏底部(setCenter) -----> 渐显(fadeIn) -----> 渐显完毕.调用回调函数_callback ----->开始倒计时渐隐时间(setTimeout(fadeOut, time)), 并绑定实时检测函数(scroll) -----> 到达自定义时间隐藏广告(fadeOut)使用说明实例化函数.传入广告容器ID.设置默认属性.
默认属性有:复制代码代码如下:delay: 20, // 调整速率fadeTime: 1 // 自动消失时间(s) var newAd = 'start';document.getElementById('show').onclick = function() {if(newAd == 'start') {newAd = floatAd.init('ad', { fadeTime: 10 });}}这里为了演示方便.所以当点击按钮时候才初始化广告.也可以在window.onload的时候就载入广告.
演示下载地址居中显示的漂浮广告代码