<form name="form5" id="form5" method="post" action="#"> 
<input type="file" name="file5" id="file5" onchange="preview5()"/> 
</form> 
<script type="text/
javascript"> 
function preview5(){ 
var x = document.getElementById("file5"); 
 if(!x || !x.value) return; 
var patn = /.jpg$|.jpeg$|.gif$/i; 
if(patn.test(x.value)){  
var y = document.getElementById("img5"); 
if(y){ 
y.src = "file://localhost/" + x.value; 
}else{ 
var img=document.createElement("img"); 
img.setAttribute("src","file://localhost/"+x.value); 
img.setAttribute("width","120"); 
img.setAttribute("height","90"); 
img.setAttribute("id","img5"); 
document.getElementById("form5").appendChild(img); 
 } 
}else{ 
alert("本地预览图片有问题哦!"); 
}} 
</script>