Option Explicit 
On Error Resume Next
Sub include(vbs)
 Dim fso : Set fso = CreateObject("scripting.FileSystemObject")
 Dim p : p   = Split(Wscript.ScriptFullName,"\")
 p(UBound(p))  = vbs
 p     = Join(p,"\")
 Dim f : Set f  = fso.OpenTextFile(p)
 Execute f.ReadAll()
' ExecuteGlobal f.ReadAll()
 f.Close()
 Set f = Nothing
 Set fso = Nothing 
' Wscript.Echo(p)
End Sub

include("1.vbs")
include("2.vbs")
'If Err Then
' Wscript.Echo(Err.description)
' Wscript.Quit()
'End If 
Wscript.Echo(a+b)

'1.vbs
'a = 3
'
'2.vbs
'b = 4