js实现上传图片实时预览，兼容chrome IE firefox多浏览器

本文链接：https://blog.youkuaiyun.com/hnxuwei/article/details/50595426

本文提供了一种在网页中实现图片上传并进行本地预览的方法，适用于一张或多张图片的实时预览。代码中详细展示了如何使用HTML和JavaScript来完成这一功能，并特别考虑了不同浏览器之间的兼容性。

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直接上代码吧，一张图、多张图，都比较适用

<html>
<head>     
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />     
<title>图片上传本地预览</title>     
<style type="text/css">
.imgDiv{width:260px;height:190px;border:1px solid #000;overflow:hidden;}
.imghead {filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod=image);}
</style>
<script type="text/javascript">


         //图片上传预览    IE是用了滤镜。
        function previewImage(file,imgDiv,imgId){
        //file表单，图片显示div，图片id
          var MAXWIDTH  = 260; 
          var MAXHEIGHT = 180;
          var div = document.getElementById(imgDiv);
          if (file.files && file.files[0])
          {
              div.innerHTML ='<img class="imghead" id='+imgId+'>';
              var img = document.getElementById(imgId);
              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 class="imghead" id='+imgId+'>';
            var img = document.getElementById(imgId);
            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-left:"+rect.left+"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>     
</head>     
<body>
<div class="imgDiv" id="d0"></div>
<input type="file" onchange="previewImage(this,'d0','img0')" />  
<div class="imgDiv" id="d1"></div>
<input type="file" onchange="previewImage(this,'d1','img1')" />  
<div class="imgDiv" id="d2"></div>
<input type="file" onchange="previewImage(this,'d2','img2')" />
<div class="imgDiv" id="d3"></div>
<input type="file" onchange="previewImage(this,'d3','img3')" />

</body>     
</html>