纯JS实现的批量图片预览加载功能

1.实现原理直接见代码,需要一张转圈的小图片,需要预览的所有图片默认的位置全是这张小图片,滚轮滚到原图需要出现的位置时候,预览加载替换小图片.实现效果

<div style="height: 2500px;" id="txtScrollTop"> 
</div> 
<div id="galleryList"> 
</div>

var util = { 
$: function (id) { 
return document.getElementById(id); 
}, 
getElementsByClassName: function (oElm, strTagName, strClassName) { 
var arrElements = oElm.getElementsByTagName(strTagName); 
var arrReturnElements = new Array(); 
strClassName = strClassName.replace(/-/g, "\-"); 
var oRegExp = new RegExp("(^|\\s)" + strClassName + "(\\s|$)"); 
var oElement; 
for (var i = 0; i < arrElements.length; i++) { 
oElement = arrElements[i]; 
if (oRegExp.test(oElement.className)) { 
arrReturnElements.push(oElement); 
} 
} 
return arrReturnElements; 
}, 
getXY: function (obj) { 
var sumTop = 0, sumLeft = 0; 
while (obj != document.body) { 
sumLeft += obj.offsetLeft; 
sumTop += obj.offsetTop; 
obj = obj.offsetParent; 
} 
return { x: sumLeft, y: sumTop } 
} 
}; var GalleryViewer = { 
GalleryContainer: {}, 
smallImgs: [], //小图片数组 
orginalImgs: [], //原始图片数组 
init: function (id, imgs, classname, smallImgSrc) { 
this.GalleryContainer = util.$(id); 
this.orginalImgs = imgs; 
for (var i = 0; i < imgs.length; i++) { //追加所有预览小图片 
var img = document.createElement("img"); 
img.src = smallImgSrc; 
img.className = classname; 
this.GalleryContainer.appendChild(img); 
} 
this.smallImgs = util.getElementsByClassName(util.$(id), "img", classname); 
if (util.getXY(GalleryViewer.GalleryContainer).y < window.screen.height) {//如果初始在页面开始部位直接预览加载 
this.preloadImages(); 
} 
var mousewheelevt = (/Firefox/i.test(navigator.userAgent)) ? "DOMMouseScroll" : "mousewheel" //FF doesn't recognize mousewheel as of FF3.x 
if (document.attachEvent) //if IE (and Opera depending on user setting) 
document.attachEvent("on" + mousewheelevt, GalleryViewer.orginalImgsAppear); 
else if (document.addEventListener) //WC3 browsers 
document.addEventListener(mousewheelevt, GalleryViewer.orginalImgsAppear, false); 
}, 
preloadImages: function () { 
for (var i = 0; i < GalleryViewer.orginalImgs.length; i++) { 
(function (i) { 
var imagePreload = new Image(); 
imagePreload.src = GalleryViewer.orginalImgs[i]; //预加载大图片 
if (imagePreload.complete) { // 如果图片已经存在于浏览器缓存，直接调用回调函数 
GalleryViewer.ImgsChange(i, imagePreload); 
return; // 直接返回，不用再处理onload事件 
} 
imagePreload.onload = GalleryViewer.ImgsChange(i, imagePreload); //加载完成替换 
})(i); 
} 
}, 
ImgsChange: function (i, obj) { 
this.smallImgs[i].src = obj.src; 
}, 
orginalImgsAppear: function () { 
//alert(getXY(this.GalleryContainer).y - window.screen.height); 
if (document.documentElement.scrollTop > util.getXY(GalleryViewer.GalleryContainer).y - window.screen.height) { 
GalleryViewer.preloadImages(); 
} 
} 
}; 
(function () { 
var imgs1 = ['../Content/images/gb_tip_layer.png', '../Content/images/gb_tip_layer.png', '../Content/images/gb_tip_layer.png']; 
GalleryViewer.init("Div1", imgs1, "smallImgs1", "../Content/images/preload.gif"); 
//参数函数分别为div.id容器,原图地址数组,小图的类名,小图地址,具体图片地址请参照自己的项目 
})();