JavaScript类型检查Request值 [英] JavaScript typeof checking a Request value
问题描述
大家好！
我在asp页面中有以下代码，其语言标记为：
<％@ LANGUAGE =" JAVASCRIPT" CODEPAGE =" 65001"％>
//查找请求变量。
var edition = Request.Form（" edition"）;
var language = Request.Form（" language"）;
Response.Write（" Edition is type& quot;" +（typeof edition）+" & quot;和
value& quot;" + edition +"& quot;< br>"）;
Response.Write（" ;语言类型& quot;" +（typeof language）+"& quot;
和value& quot;" + language +"& quot;< br> ;"）;
if（edition ==" undefined" ||
（typeof edition）==" undefined"）
{
Response.Write（" Choose Page< br>"）;
Server.Execute（" choosePage.asp"）;
} //结束如果
其他
{
Response.Write（" View Page< br>" ;）;
Server.Execute（" viewPage.asp"）;
} //结束其他
问题在于我所看到的：
版本是类型对象和值undefined
语言是类型对象和价值undefined
查看页面
choosePage.asp或viewPage.asp中没有任何内容，但我无法支付
找出为什么其他是触发而不是if - 我打印出的
版本var显示它的值为undefined......
任何帮助都将非常感激！
Rob
:)
Hi All!
I have the following code in an asp page whose language tag is:
<%@LANGUAGE="JAVASCRIPT" CODEPAGE="65001"%>
// Find request variables.
var edition = Request.Form ("edition");
var language = Request.Form ("language");
Response.Write("Edition is type "" + (typeof edition) + "" and
value "" + edition + ""<br>");
Response.Write("Language is type "" + (typeof language) + ""
and value "" + language + ""<br>");
if (edition == "undefined" ||
(typeof edition) == "undefined")
{
Response.Write("Choose Page<br>");
Server.Execute ("choosePage.asp");
} // end if
else
{
Response.Write("View Page<br>");
Server.Execute ("viewPage.asp");
} // end else
The problem is this is what I see:
Edition is type "object" and value "undefined"
Language is type "object" and value "undefined"
View Page
There is nothing in choosePage.asp or viewPage.asp yet, but I am unable to
figure out why the else is triggering and not the if - my print out of the
edition var shows it has a value of "undefined"...
Any help would be most appreciated!
Rob
:)
推荐答案
" Robert Mark Bram" <再******** @ removethis.optushome.com.au>写道：
"Robert Mark Bram" <re********@removethis.optushome.com.au> writes:
Response.Write（" Edition is type& quot;" +（typeof edition）+"& quot; and
value& quot ;" + edition +"& quot;< br>"）;
.... if（edition ==" undefined" ||
（typeof edition）==" undefined"）
.... Edition是type" object"和值未定义
因此，版本是*对象*，当它转换为字符串时，它将成为字符串未定义。即，edition.toString（）==" undefined"。
然后测试是否版本==未定义。 。它不是，因为它是一个
对象，而不是字符串，对象只等于它们。
同样，（typeof edition） =="未定义"因为（typeof
edition）==" object"。
但是我无法弄清楚为什么其他是触发而不是
如果 - 我打印出的版本var显示它的值为
undefined...
Response.Write("Edition is type "" + (typeof edition) + "" and
value "" + edition + ""<br>"); .... if (edition == "undefined" ||
(typeof edition) == "undefined") .... Edition is type "object" and value "undefined"
So, edition is an *object*, and when it is converted to a string, it
becomes the string "undefined". I.e., edition.toString() == "undefined".
You then test whether edition=="undefined" . It isn''t, since it is an
object, not a string, and objects are only equal to themselves.
Likewise, (typeof edition)=="undefined" fails since (typeof
edition)=="object".
but I am unable to figure out why the else is triggering and not the
if - my print out of the edition var shows it has a value of
"undefined"...
不，它的值是一个对象，这是值未定义都不是或者
字符串undefined。该对象有一个名为toString的方法，
返回字符串undefined。
/ L
-
Lasse Reichstein Nielsen - lr*@hotpop.com
Art D''HTML：< ; URL：http：//www.infimum.dk/HTML/randomArtSplit.html>
''没有判断的信仰只会降低精神神圣。''
No, its value is an object, which is neither the value "undefined" or
the string "undefined". That object has a method called toString that
returns the string "undefined".
/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
Art D''HTML: <URL:http://www.infimum.dk/HTML/randomArtSplit.html>
''Faith without judgement merely degrades the spirit divine.''
Hi Lasse - 感谢您的回复！
Hi Lasse - thank you for your response!
Response.Write（" Edition is type& quot ;" +（typeof edition）+"& quot;
和value& quot;" + edition +"& quot;< br>"）;
Response.Write("Edition is type "" + (typeof edition) + "" and value "" + edition + ""<br>");
...
...
if（edition ==" undefined" ||
（typeof edition）==" undefined"）
if (edition == "undefined" ||
(typeof edition) == "undefined")
...
...
Edition是type" object"和值undefined
Edition is type "object" and value "undefined"
因此，edition是一个* object *，当它转换为字符串时，它将成为字符串undefined。即，edition.toString（）==" undefined"。
So, edition is an *object*, and when it is converted to a string, it
becomes the string "undefined". I.e., edition.toString() == "undefined".
我刚试过这个并且让事情变得更加混乱：
if（edition.toString（）==" undefined"）
{
Response.Write（" Choose Page< br>"）;
Server.Execute（" choosePage.asp"）;
} //结束如果
else
{
Response.Write（" View Page< br>"）;
Server.Execute（" viewPage.asp"）;
} //结束其他
结果错误：
错误类型：
Microsoft JScript运行时（0x800A01B6）
对象不支持此属性或方法
/polyprint/newsletter.asp，第16行
第16行是行：
if（edition.toString（）==" undefined"）
它怎么可能是一个对象而没有toString？
Rob
:)
I just tried this and got something even more confusing:
if (edition.toString() == "undefined")
{
Response.Write("Choose Page<br>");
Server.Execute ("choosePage.asp");
} // end if
else
{
Response.Write("View Page<br>");
Server.Execute ("viewPage.asp");
} // end else
The resulting error:
Error Type:
Microsoft JScript runtime (0x800A01B6)
Object doesn''t support this property or method
/polyprint/newsletter.asp, line 16
Line 16 is the line:
if (edition.toString() == "undefined")
How can it be an Object and not have toString?
Rob
:)
" Robert M ark Bram <再******** @ removethis.optushome.com.au>写道：
"Robert Mark Bram" <re********@removethis.optushome.com.au> writes:
我只是尝试了这个并且让事情变得更加混乱：
确实！
if（edition .toString（）==" undefined"）
....结果错误：
错误类型：
Microsoft JScript运行时（0x800A01B6）
对象不支持这个属性或方法
/polyprint/newsletter.asp，第16行
第16行是行：
if（edition.toString（）==" undefined"）
如何成为一个Object而不是toString？
I just tried this and got something even more confusing:
Indeed!
if (edition.toString() == "undefined") .... The resulting error:
Error Type:
Microsoft JScript runtime (0x800A01B6)
Object doesn''t support this property or method
/polyprint/newsletter.asp, line 16
Line 16 is the line:
if (edition.toString() == "undefined")
How can it be an Object and not have toString?
有一个值为object的类型的值这不是一个对象：
null值。但是，将其转换为字符串会给出null，而不是
" undefined" （至少它应该符合ECMAScript标准）。
所有Javascript对象都有一个原型链，结尾于
Object.prototype，它有一个toString方法。但是，本机
对象几乎可以任意奇怪。
试试这个：
if（edition == = undefined）{
Response.Write（" undefined< br>"）;
}
if（edition === null ）{
Response.Write（" null< br>"）;
}
if（"" + edition = =" undefined"）{
Repsonse.Write（" string：undefined< br>"）;
}
if（ edition！== undefined&& edition！== null）{
for（var i in edition）{
Response.Write（i +" =" ; +版[i] +"< br>）;
}
}
如果是对象无论如何，这可能会说明它是什么物品。
/ L
-
Lasse Reichstein Nielsen - lr*@hotpop.com
Art D''HTML： <的URL：http：//www.infimum.dk/HTML/randomArtSplit.html>
''没有判断的信仰只会降低精神神圣。''
There is one value with a typeof of "object" that isn''t an object: the
null value. However, converting that to a string gives "null", not
"undefined" (at least it should according to the ECMAScript standard).
All Javascript objects have a prototype chain that ends at
Object.prototype, which has a toString method. However, native
objects can act almost arbitrarily strange.
Try this:
if (edition === undefined) {
Response.Write("undefined<br>");
}
if (edition === null) {
Response.Write("null<br>");
}
if (""+edition == "undefined") {
Repsonse.Write("string:undefined<br>");
}
if (edition !== undefined && edition !== null) {
for(var i in edition) {
Response.Write(i+"="+edition[i]+"<br>);
}
}
If it is an object of any kind, this might shed some light on which
kind of object it is.
/L
--
Lasse Reichstein Nielsen - lr*@hotpop.com
Art D''HTML: <URL:http://www.infimum.dk/HTML/randomArtSplit.html>
''Faith without judgement merely degrades the spirit divine.''
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