Can I include a file in both server-side and client-side script?

Often, ASP developers want to put common functions in a place accessible to both client-side and server-side scripts. There are some challenges with this, including the fact that several server-side objects (such as Response, Request) are not available on the client, much like several client-side elements (such as document, window and msgbox) are not available on the server. But if you write a routine that's generic enough, it can make sense to have it serve both the client-side and server-side scripts - reducing maintenance in the long run. 
 
 
If you're using IIS 5.0 or better, you can achieve this simply as follows. Let's say you have a .js file called 'whatever.js': 
 

function returnValue() { return "value"; }

 
Now you can call this from both server-side and client-side JScript like this: 
 

<script language=jscript runat=server src=whatever.js></script>    <script language=jscript runat=server>  Response.Write("Server: "+returnValue()+"<br>");  </script>    <script language=jscript src=whatever.js></script>    <script language=jscript>  document.write("Client: "+returnValue());  </script>

 
Now, for those using IIS 4.0: 
 
I'm going to provide an example of using a VBScript routine in server-side and client-side VBScript, as well as using a JScript routine in server-side and client-side JScript. I'm not going to attempt to crosswire the languages, nor am I going to try to deal with workarounds for swapping out document / response depending on the scope. 
 
Here is an example of using a VBScript routine in client-side and server-side script. You'll need a file called fixString.asp: 
 

<%      function fixString(str)          fixString = replace(str,"Bob","the coder formerly known as Bob")      end function  %>

 
And another ASP file, with this code: 
 

<!--#include file='fixString.asp'-->  <%      response.write fixString("Do you think that's okay with Bob?")      set fso = CreateObject("scripting.FileSystemObject")      set fs = fso.OpenTextFile(server.MapPath("fixString.asp"))      f = fs.ReadAll()      fs.close: set fs = nothing: set fso = nothing        ' we just replace the server-side delimiters with client tags      f = replace(f,"<" & "%","<" & "script language=vbscript>")      f = replace(f,"%" & ">","</script>")      response.write(f)  %>    <script language=vbscript>      msgbox fixString("I don't think Bob will mind."),64,"Bob"  </script>

 
Here is an example of using a JScript routine in client-side and server-side script. You'll need a file called fixStringJS.asp: 
 

<script language=JScript runat=server>  function fixString(str)  {      return str.replace("Bob","the coder formerly known as Bob");  }  </script>

 
And another ASP file, with this code: 
 

<!--#include file='fixStringJS.asp'-->  <Script language=JScript runat=server>      Response.Write(fixString("Do you think that's okay with Bob?"));      var fso = new ActiveXObject("Scripting.FileSystemObject");      var fs = fso.OpenTextFile(Server.MapPath("fixStringJS.asp"));      var f = fs.ReadAll();      fs.close(); var fs = null; var fso = null;        f = f.replace(" runat=server","");      Response.Write(f);  </script>    <script language=Jscript>      alert(fixString("I don't think Bob will mind."));  </script>

 
Now, this fictitious example doesn't deal with a serious limitation in JScript's implementation of replace - it only replaces the *first* instance of the search string, not *all* instances (like VBScript). Not sure which language implemented it wrong; according to the ECMA docs, JScript is correct. But I prefer the behavior of VBScript. I'll leave it as an exercise to the reader to code a workaround in JScript.