浏览器 本地预览图片 window.url.createobjecturl

第一种方式

<script type="text/javascript">   
function setImagePreview() {   
var docObj = document.getElementById("ctl00_ContentMain_file_head");   
var fileName = docObj.value;   
if (!fileName.match(/.jpg|.gif|.png|.bmp/i)) {   
alert('您上传的图片格式不正确，请重新选择！');   
return false;   
}   
  
var imgObjPreview = document.getElementById("preview");   
if (docObj.files && docObj.files[0]) {   
//火狐下，直接设img属性   
imgObjPreview.style.display = 'block';   
imgObjPreview.style.width = '63px';   
imgObjPreview.style.height = '63px';   
//imgObjPreview.src = docObj.files[0].getAsDataURL();   
if (window.navigator.userAgent.indexOf("Chrome") >= 1 || window.navigator.userAgent.indexOf("Safari") >= 1) {   
imgObjPreview.src = window.webkitURL.createObjectURL(docObj.files[0]);   
}   
else {   
imgObjPreview.src = window.URL.createObjectURL(docObj.files[0]);   
}   
} else {   
//IE下，使用滤镜   
docObj.select();   
docObj.blur();   
var imgSrc = document.selection.createRange().text;   
var localImagId = document.getElementById("localImag");   
//必须设置初始大小   
localImagId.style.width = "63px";   
localImagId.style.height = "63px";   
//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;   
} 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();   
}   
return true;   
}   
  
</script>   

<div id="localImag"><img id="preview" width="-1" height="-1" style="display:none" /></div> 
<asp:FileUpload ID="file_head" runat="server" onchange="javascript:setImagePreview();" />

第二种方式

function setImagePreview(a,b) {
    var url ='';
    if (navigator.userAgent.indexOf("MSIE")>=1) { // IE
        url = document.getElementById(a).value;
    } else if(navigator.userAgent.indexOf("Firefox")>0) { // Firefox
        url = window.URL.createObjectURL(document.getElementById(a).files.item(0));
    } else if(navigator.userAgent.indexOf("Chrome")>0) { // Chrome
        url = window.URL.createObjectURL(document.getElementById(a).files.item(0));
    }
    var imgPre = document.getElementById(b);
    imgPre.src = url;
}

a = fileid

b=imgid