Try-Catch-End Try in VBScript doesn't seem to work - vbscript

Question

I'm trying the following code:
Try ' DOESN'T WORK
Throw 2 ' How do I throw an exception?
Catch ex
'What do I do here?
End Try
but I'm getting the error Statement expected in the catch clause.
Does anyone know how I can catch/throw exceptions in VBScript using try/catch? (I am not looking for solutions with On Error Do X.)

Answer 1

Handling Errors
A sort of an "older style" of error handling is available to us in VBScript, that does make use of On Error Resume Next. First we enable that (often at the top of a file; but you may use it in place of the first Err.Clear below for their combined effect), then before running our possibly-error-generating code, clear any errors that have already occurred, run the possibly-error-generating code, and then explicitly check for errors:
On Error Resume Next
' ...
' Other Code Here (that may have raised an Error)
' ...
Err.Clear ' Clear any possible Error that previous code raised
Set myObj = CreateObject("SomeKindOfClassThatDoesNotExist")
If Err.Number <> 0 Then
WScript.Echo "Error: " & Err.Number
WScript.Echo "Error (Hex): " & Hex(Err.Number)
WScript.Echo "Source: " & Err.Source
WScript.Echo "Description: " & Err.Description
Err.Clear ' Clear the Error
End If
On Error Goto 0 ' Don't resume on Error
WScript.Echo "This text will always print."
Above, we're just printing out the error if it occurred. If the error was fatal to the script, you could replace the second Err.clear with WScript.Quit(Err.Number).
Also note the On Error Goto 0 which turns off resuming execution at the next statement when an error occurs.
If you want to test behavior for when the Set succeeds, go ahead and comment that line out, or create an object that will succeed, such as vbscript.regexp.
The On Error directive only affects the current running scope (current Sub or Function) and does not affect calling or called scopes.
Raising Errors
If you want to check some sort of state and then raise an error to be handled by code that calls your function, you would use Err.Raise. Err.Raise takes up to five arguments, Number, Source, Description, HelpFile, and HelpContext. Using help files and contexts is beyond the scope of this text. Number is an error number you choose, Source is the name of your application/class/object/property that is raising the error, and Description is a short description of the error that occurred.
If MyValue <> 42 Then
Err.Raise(42, "HitchhikerMatrix", "There is no spoon!")
End If
You could then handle the raised error as discussed above.
Change Log
Edit #1:
Added an Err.Clear before the possibly error causing line to clear any previous errors that may have been ignored.
Edit #2:
Clarified.
Edit #3:
Added comments in code block. Clarified that there was expected to be more code between On Error Resume Next and Err.Clear. Fixed some grammar to be less awkward. Added info on Err.Raise. Formatting.

Answer 2

VBScript doesn't have Try/Catch. (VBScript language reference. If it had Try, it would be listed in the Statements section.)
On Error Resume Next is the only error handling in VBScript. Sorry. If you want try/catch, JScript is an option. It's supported everywhere that VBScript is and has the same capabilities.

Answer 3

Try Catch exists via workaround in VBScript:
http://web.archive.org/web/20140221063207/http://my.opera.com/Lee_Harvey/blog/2007/04/21/try-catch-finally-in-vbscript-sure
Class CFunc1
Private Sub Class_Initialize
WScript.Echo "Starting"
Dim i : i = 65535 ^ 65535
MsgBox "Should not see this"
End Sub
Private Sub CatchErr
If Err.Number = 0 Then Exit Sub
Select Case Err.Number
Case 6 WScript.Echo "Overflow handled!"
Case Else WScript.Echo "Unhandled error " & Err.Number & " occurred."
End Select
Err.Clear
End Sub
Private Sub Class_Terminate
CatchErr
WScript.Echo "Exiting"
End Sub
End Class
Dim Func1 : Set Func1 = New CFunc1 : Set Func1 = Nothing

Answer 4

Sometimes, especially when you work with VB, you can miss obvious solutions. Like I was doing last 2 days.
the code, which generates error needs to be moved to a separate function. And in the beginning of the function you write On Error Resume Next. This is how an error can be "swallowed", without swallowing any other errors. Dividing code into small separate functions also improves readability, refactoring & makes it easier to add some new functionality.