js上传图片前进行预览

<script type="text/javascript">  

   //图片上传预览    IE是用了滤镜。    

function previewImage(file) {    

     var MAXWIDTH = 260;    

     var MAXHEIGHT = 180;     

    var div = document.getElementById('preview');     

    if (file.files && file.files[0]) {        

     div.style.display = "block";          

    div.innerHTML = '<img id=imghead>';      

    var img = document.getElementById('imghead');     

    img.onload = function () {          

       var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);    

       img.width = rect.width;          

       img.height = rect.height;       

      //img.style.marginLeft = rect.left+'px';     

       img.style.marginTop = rect.top + 'px';    

         }     

        var reader = new FileReader();    

       reader.onload = function (evt) { img.src = evt.target.result;}      

       reader.readAsDataURL(file.files[0]);   

  }      

   else //兼容IE         {         

    var sFilter = 'filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=scale,src="';      

    file.select();        

    var src = document.selection.createRange().text;  

    div.innerHTML = '<img id=imghead>';    

         var img = document.getElementById('imghead');  

           img.filters.item('DXImageTransform.Microsoft.AlphaImageLoader').src = src;    

         var rect = clacImgZoomParam(MAXWIDTH, MAXHEIGHT, img.offsetWidth, img.offsetHeight);    

         status = ('rect:' + rect.top + ',' + rect.left + ',' + rect.width + ',' + rect.height);        

     div.innerHTML = "<div id=divhead style='width:" + rect.width + "px;height:" + rect.height + "px;margin-top:" + rect.top + "px;" + sFilter + src + "\"'></div>";     

    }  

   }   

  function clacImgZoomParam(maxWidth, maxHeight, width, height) {    

     var param = { top: 0, left: 0, width: width, height: height };     

    if (width > maxWidth || height > maxHeight) {        

     rateWidth = width / maxWidth;       

      rateHeight = height / maxHeight;

            if (rateWidth > rateHeight) {       

          param.width = maxWidth;            

     param.height = Math.round(height / rateWidth);      

       } else {              

   param.width = Math.round(width / rateHeight);       

          param.height = maxHeight;         

    }      

   }

  param.left = Math.round((maxWidth - param.width) / 2);     

    param.top = Math.round((maxHeight - param.height) / 2);   

      return param;     }

</script>

<style type="text/css">
    #preview { overflow:hidden; display:none;}
    #imghead { filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>

<div><input id="fileImg" name="fileImg" οnchange="previewImage(this)" type="file" runat="server" /></div>
            <div id="preview">
                <img id="imghead" width=100 height=100 border=0 src='' />
            </div>

转载于:https://www.cnblogs.com/zhftyy/p/5141993.html