js 对象是否存在判断

复制代码代码如下:
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<title>javascript object</title>
<body>
<input id="aaa">
<input type=button onclick="check（"aaa"）" value="checkaaa">
<input type=button onclick="check（"aaffdssfg"）" value="checkother">
<script language="javascript">
<！--
function check（strObj）
{
if（typeof（eval（"document.all."+strObj））！= "undefined"）
{
alert（strObj +" is an object"）;
}
else
{
alert（strObj +" is not an object"）;
}
}
//-->
</script>
</body>