JS实现图片上传后多图片尺寸预览功能

      前段时间做了一个会员头像上传，能自动生成多尺寸预览效果，当然如果你并不需要那么多尺寸的预览效果就用一个预览区即可。刚开始考虑采用ajax调用，但前台数据需要点击提交才能调用数据库内容，并不是同步预览，这条路并不通，因此还是采用JS的方法。

JS部分

       先引用公共JS库，下面增加

<script type="text/javascript">
<!--
//下面用于图片上传预览功能
function setImagePreview(avalue){
 var docObj=document.getElementById("face");//上传元素ID
 var imgObjPreview=document.getElementById("preview");
 var imgObjPreview=document.getElementById("preview2");
 var imgObjPreview=document.getElementById("preview3");
 if(docObj.files &&docObj.files[0])
 {
 //火狐下，直接设img属性
 imgObjPreview.style.display = 'block';
 imgObjPreview.style.width = '150px';
 imgObjPreview.style.height = '150px';
 imgObjPreview2.style.display = 'block';
 imgObjPreview2.style.width = '110px';
 imgObjPreview2.style.height = '110px';
 imgObjPreview3.style.display = 'block';
 imgObjPreview3.style.width = '40px';
 imgObjPreview3.style.height = '40px';
 //imgObjPreview.src = docObj.files[0].getAsDataURL();
 //火狐7以上版本不能用上面的getAsDataURL()方式获取，需要以下方式
 imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);
 imgObjPreview2.src = window.URL.createObjectURL(docObj.files[0]);
 imgObjPreview3.src = window.URL.createObjectURL(docObj.files[0]);
 }
 else
 {
 //IE下，使用滤镜
 docObj.select();
 var imgSrc = document.selection.createRange().text;
 var localImagId = document.getElementById("localImag");
 var localImagId2 = document.getElementById("localImag2");
 var localImagId3 = document.getElementById("localImag3");
 //必须设置初始大小
 localImagId.style.width = "150px";
 localImagId.style.height = "150px";
 localImagId2.style.width = "110px";
 localImagId2.style.height = "110px";
 localImagId3.style.width = "40px";
 localImagId3.style.height = "40px";
 //图片异常的捕捉，防止用户修改后缀来伪造图片
 try{
 localImagId.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
 localImagId.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
 localImagId2.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
 localImagId2.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
 localImagId3.style.filter="progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale)";
 localImagId3.filters.item("DXImageTransform.Microsoft.AlphaImageLoader").src = imgSrc;
 }
 catch(e){  
 alert("您上传的图片格式不正确，请重新选择!");
 return false;
 }
 imgObjPreview.style.display = 'none'; document.selection.empty(); 
 imgObjPreview2.style.display = 'none'; document.selection.empty(); 
 imgObjPreview3.style.display = 'none'; document.selection.empty(); 
 } 
 return true;
}
-->
</script>

HTML部分

<p class="fieldbtn">
 <input name="face" type="file" id="face" size="45" onchange="javascript:setImagePreview();"/>
</p>
<p id="localImag" >
 <img id="preview" src="images/view.png" width="150" height="150"/>
 <img id="preview2" src="images/view.png" width="110" height="110"/>
 <img id="preview3" src="images/view.png" width="40" height="40"/>
</p>

上传按钮CSS样式

       系统默认的上传按钮比较难看，分享案例的上传按钮样式

<style type="text/css">
.fieldbtn{width:84px;height:28px;text-align:center;border:1px solid #ccc;position:relative;overflow:hidden;display:inline-block;cursor:pointer;}
.fieldbtn input{font-size:100px;right:0;top:0;position:absolute;opacity:0;filter:alpha(opacity=0);cursor:pointer;z-index:999;}
</style>