Detecting null/empty input from user

How can I check if the user has input a开发者_如何学编程 null or empty string in classic-asp? Right now I am have this code.

If Request.Form("productId") == "" Then
'my code here
End If

But its not working.

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Classic ASP/VBScript uses one = to check for equality, not two. Another thing you may want to try is

If Request.Form("productid") = "" Then
   Code here
End If

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It is a mess. Here's what I have found ...

(1) To look for existence in the QS, use if IsEmpty(x)=false (ie, URL?x)

(2) To look for a value in the QS, look for if x <> "" (ie, URL?x=anything)

Good luck!

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If IsEmpty(Request.Form("inputPhoneNo")) = False Then
    response.Write"<script language=javaScript>alert('Blank Phone Number');</script>"
    response.Write"<script language=javascript>history.back()</script>"
Else

End If