<%@ language=JScript %>
<%
var k = Request.QueryString("key");
var s = String(k);
if (typeof(s)==undefined){
Response.Write("");
} else { Response.Write(s);}
%>
<%
var k = Request.QueryString("key");
var s = String(k);
if (typeof(s)==undefined){
Response.Write("");
} else { Response.Write(s);}
%>
if(document.dataform.key!= undefined){
test.asp?key=document.dataform.key.value
}else{
test.asp?key=
}
var k = Request.QueryString("key");
var s = String(k);
if(s==""){Response.Write(s);}else{Response.Write("undifined");}
%>
<%
var k = Request.QueryString("key");
Response.Write('typeof(k) == "undefined": ');
Response.Write(typeof(k) == "undefined");
Response.Write("<br>");
Response.Write("k == null: ");
Response.Write(k == null);
Response.Write("<br>");
Response.Write('k == undefined: ');
Response.Write(k == undefined);
Response.Write("<br>");
%>以下是我得到的输出:请求test.asp
输出
typeof(k) == "undefined": False
k == null: False
k == undefined: False请求test.asp?key=undefined
输出
typeof(k) == "undefined": False
k == null: False
k == undefined: False我不知道还有什么可以区别开着两种情况?
undefined //此undefied,用typeof undefined,得到的结果为真,它是关键字代表无效的值
请求test.asp?key=undefined时,输出
undefined//代表字符串"undefined"