控制input框只读可以防止用户对数据的更改，在某些情况下还是比较实用的，下面使用js来完成这个只读实现
代码如下:
<html>
<head>
<title> New Document </title>
<meta name="Generator" content="EditPlus">
<meta name="Author" content="">
<meta name="Keywords" content="">
<meta name="Description" content="">
</head>
<script language="JavaScript">
function isreadonly(){
var obj = document.getElementById("username");
obj.setAttribute("readOnly",true);
obj.style.backgroundColor="#d2d2d2";
}
function readwrite(){
var obj = document.getElementById("username");
obj.setAttribute("readOnly",false);
obj.style.backgroundColor="#ffffff";
}
</script>
<body>
<form name="addform" id="addform" method="post" action="" >
<input type="text" id="username" name="username">
<input type="button" name="只读" value="read" onclick="isreadonly();">
<input type="button" name="可写" value="write" onclick="readwrite();">
</form>
</body>
</html>
<!--
点击“read”按钮，input框不能书写，且变灰；点击“write”按钮，input框恢复。
-->