Optional parameters in ASP VBScript functions

[RonaldSchultz]

VBScript does not natively support optional function parameters, which can be a problem. Over the years, a number of workarounds have been proposed, but these workarounds tend to be a bit complex.
Some workarounds are detailed here: [URL unfurl="true"]http://www.advancedqtp.com/optional-parameters/[/url]
and here: [URL unfurl="true"]http://www.tek-tips.com/viewthread.cfm?qid=1329150[/url]

Fortunately, there is another partial workaround that does not appear to be widely known. This workaround does not support differing numbers of parameters, but it does support optional parameter values.

Using [tt]VarType()[/tt] in the function body, it is possible to test whether a value was supplied in the function call before any attempt is made to use that value.

For example:

[pre]function FunctionName(arg1, arg2)
dim var1
'test to see whether arg1 is supplied as a string
if VarType(arg1) <> 8 then
var1 = "default value"
else
var1 = arg1
end if
...
end function[/pre]

Thus, [tt]FunctionName[/tt] may be called with or without a 1st parameter value:

[pre]call FunctionName("val1", "val2")

call FunctionName( , "val2")[/pre]

In this example, the optional parameter is expected as a string (type value = 8). Missing parameter values have a type value of 10. A full list of type values may be found on Microsoft’s web site: [URL unfurl="true"]http://msdn.microsoft.com/en-us/library/3kfz157h%28v=vs.84%29.aspx[/url]

A limitation of this workaround is that it does not work for the last parameter in the list.

 

[SkipVought]

Ron,

Welcome to Tek-Tips!

You oughta look around a bit and get to know the lay of the land.

You might consider putting your bright idea into a FAQ, which would be a much more useful place, as this will eventually be buried under other posts.

Skip,
[sub]
Just traded in my OLD subtlety...
for a NUance![/sub]