js给指定id的div下面创建元素

<script language="javascript" type="text/javascript">
var count=0 ;
function additem(id){
count ++;
var cell;
cell = document.getElementById(id);
var unit = document.createElement("div");
unit.className = "unit";
unit.id=count;
cell.appendChild(unit);
var label = document.createElement("label");
label.innerHTML ="选项"+count;
unit.appendChild(label);
var childEles = document.getElementById(count);
var input = document.createElement('input');
input.setAttribute("type", "text");
input.setAttribute("name","content"+count);


input.className = "textInput";
var input1 = document.createElement('input');
input1.setAttribute("type", "button");
input1.setAttribute("value","删除");
input1.setAttribute('onclick',"deleteitem(this,"+count+")");
//var inner = "<input id=\"St"+count+"\" type=\"text\" name=\"St"+count+"\" value= \"St"+count+"\"><input type=\"button\" value=\"删除\" onclick=\'deleteitem(this);\'>";
//var inner = '<input id=St'+count+' type="text" name=St'+count+' value= St'+count+'><input type="button" value="删除" onClick="deleteitem(this)">';
childEles.appendChild(input);
childEles.appendChild(input1);

var size ="content"+count;
//document.getElementById('size').value += size;

if(document.getElementById('size').value == ''){
document.getElementById('size').value += size; 
}else{
document.getElementById('size').value = document.getElementById('size').value + "," + size;
}

}
function deleteitem(obj,count)
{
var tb = document.getElementById('tb');
    var Row = obj.parentNode;
    tb.removeChild(Row);


}
</script>

<form method="post" action="__URL__/add_query/__MODULE__?callbackType=closeCurrent" class="pageForm required-validate" enctype="multipart/form-data" onsubmit="return validateCallback(this, dialogAjaxMenu)">
<input type="hidden" name="size" id="size" value="" />

<div id="tb">

<!-- <div class="unit">
<label>选项1：</label>
<input type="text" class="required"  name="content1">
<button onclick="return add();">+</button>
</div> -->

</div>

<div class="formBar">
<ul>
<li><div><input name="button" type="button" onclick='additem("tb")' value="添加>>"/></div></li>
<li><div class="buttonActive"><div class="buttonContent"><button type="submit" onclick="javascript:window.close();">保存</button></div></div></li>
<li><div class="button"><div class="buttonContent"><button type="button" class="close">取消</button></div></div></li>
</ul>
</div>

</form>