JS控制文本域只读或可写属性的方法

<input id="username" name="userneme" type="text" style="width:50px" size=106>
密码:<input id="userpwd" type="text" name="userpwd" size=106 style="width:50px">
<input name="content" type="checkbox")" value="checkbox" onclick="changeCheck()"/>
匿名发表(免注册)
<SCRIPT LANGUAGE="JavaScript">
<!--
function changeCheck()
{
var aa=document.getElementById("username");
var bb=document.getElementById("userpwd");
var =document.getElementById("content");
if(.checked)
{
aa.readonly=true;
bb.readonly=true;
aa.disabled = true;
bb.disabled = true;
}
else
{
aa.readonly=false;
bb.readonly=false;
aa.disabled = false;
bb.disabled = false;
}
}
//-->
</SCRIPT>