try:
<script>
//var Login=true
if(typeof(Login)!='undefined') alert("login");
else alert("Not login");
</script>
<script>
//var Login=true
if(typeof(Login)!='undefined') alert("login");
else alert("Not login");
</script>
try{
Login=Login+1;
}catch(e){
alert("Login 没有定义;")
}