html

<input type="button" name="button" value="添加附件" onclick="addInput()">
<input type="button" name="button" value="删除附件" onclick="deleteInput()">
<span id="upload"></span>

js

<script type="text/javascript">
var attachname = "attach";
var i=1;
function addInput(){
if(i>0){
var attach = attachname + i ;
if(createInput(attach))
i=i+1;
}

}
function deleteInput(){
if(i>1){
i=i-1;
if(!removeInput())
i=i+1;
}
}

function createInput(nm){
var aElement=document.createElement("input");
aElement.name=nm;
aElement.id=nm;
aElement.type="file";
aElement.size="50";
//aElement.value="thanks";
//aElement.onclick=Function("asdf()");
if(document.getElementById("upload").appendChild(aElement) == null)
return false;
return true;
}

function removeInput(nm){
var aElement = document.getElementById("upload");
if(aElement.removeChild(aElement.lastChild) == null)
return false;
return true;
}

</script>

文章来源:http://www.cnblogs.com/suiqirui19872005/archive/2007/06/12/780978.html