图片上传即时显示缩略图的js代码

<script language="javascript" type="text/javascript">
 var allowExt = ["jpg", "gif", "bmp", "png", "jpeg"];
 var preivew = function（file, container）{
try{
var pic = new Picture（file, container）;
}catch（e）{
alert（e）;
}
 }
 //缩略图类定义
 var Picture = function（file, container）{
var height = 0, 
widht = 0, 
ext = "",
size = 0,
name= "",
path= "";
var self = this;
if（file）{ 
name = file.value;
if （window.navigator.userAgent.indexOf（"MSIE"）>=1）{ 
 file.select（）; 
 path = document.selection.createRange（）.text; 
}else if（window.navigator.userAgent.indexOf（"Firefox"）>=1）{ 
 if（file.files）{ 
 path = file.files.item（0）.getAsDataURL（）; 
 }else{
 path = file.value;
 }
} 
}else{
throw "bad file";
} 


ext = name.substr（name.lastIndexOf（"."）, name.length）;

if（container.tagName.toLowerCase（） ！= "img"）{
throw "container is not a valid img label";
container.visibility = "hidden";
}
container.src = path;
container.alt = name;
container.style.visibility = "visible";
height = container.height;
widht = container.widht;
size= container.fileSize;


this.get = function（name）{
return self[name];
}

this.isValid = function（）{
if（allowExt.indexOf（self.ext） ！== -1）{
 throw "the ext is not allowed to upload";
 return false;
}
}
 }
</script>
<div class="previewDemo">
 <input id="file" type="file" onchange="preivew（this, document.getElementById（"img"））;">
 <img id="img" style="visibility:hidden" height="100px" width="100px">
</div>