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JScript and VBScript Arrays

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Earlier
I alluded to the fact that JScript arrays are objects but VBScript arrays are not. What's
up with that?

It's
kind of strange. Consider the properties
of a JScript array. A Jscript array is

*
one dimensional.

*
associative; JScript arrays are indexed by strings. Numeric
indices are actually converted to strings internally.

*
sparse: arr[1]
= 123; arr[1000000] = 456; gives
you a two-member array, not a million-member array.

*
an object with properties and methods.

Whereas
a VBScript array is

*
multi-dimensional

*
indexed by integer tuples

*
dense

*
not an object

It
is hard to come up with two things that could be more different and yet both called
"array".

As
you might expect, JScript and VBScript arrays have completely different implementations
behind the scenes. A JScript array is
basically just a simple extension of the existing JScript expando object infrastructure,
which is implemented as a (rather complicated) hash table. A
VBScript array is implemented using the SAFEARRAY data structure, which is pretty
much just a structure wrapped around a standard "chunk of memory" C-style array.

Since
all the COM objects in the world expect VBScript-style arrays and not JScript-style
arrays, making JScript interoperate with COM is not always easy. I
wrote an object called VBArray into
the JScript runtime to translate VBScript-style arrays into JScript arrays, but it
is pretty kludgy. And though I wrote
some code to go the other way -- to turn JScript arrays into VBScript arrays -- there
were just too many thorny issues involving object identity and preservation of information
for us to actually turn it on. There
weren't exactly a whole lot of users demanding the feature either, so that part of
the feature got cut. (If I recall correctly,
my colleague Peter Torr wrote some COM code to do that before he came to work at Microsoft. He
might still have it lying around.)

Things
got even weirder when I wrote the code to interoperate between CLR arrays and JScript
.NET arrays, but that's another story.

Comments

  • Anonymous
    September 22, 2003
    Why are there two types of multidimentional arrays? What is the difference between the (x)(y) and (x,y) notation?dim arrBararrBar = Array(Array(1,2), Array(3,4))response.write arrBar(0)(0) & "<BR>"response.write arrBar(0)(1) & "<BR>"response.write arrBar(1)(0) & "<BR>"response.write arrBar(1)(1) & "<BR>"dim arrFoo (1,1)arrFoo (0,0) = 1arrFoo (0,1) = 2arrFoo (1,0) = 3arrFoo (1,1) = 4response.write arrFoo(0,0) & "<BR>"response.write arrFoo(0,1) & "<BR>"response.write arrFoo(1,0) & "<BR>"response.write arrFoo(1,1) & "<BR>"'these don't workresponse.write arrFoo(0)(0)response.write arrBar(0,0)

  • Anonymous
    February 10, 2004
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    thanks ur website help

  • Anonymous
    May 20, 2004
    The comment has been removed

  • Anonymous
    May 20, 2004
    Yes, it would be nice. Unfortunately, I never did get around to implementing that in JScript Classic. Sorry about that.

    I did add much better support for arrays in JScript .NET though. (Small consolation, I know.)

  • Anonymous
    April 19, 2005
    I'm one of those crazed users who's trying to figure out how to pass a JScript array argument to C# code. If I cast the argument as an object, its type is System.__COMObject, so I assume I need to marshal it somehow.

    I currently am exposing JScript methods to my C# code by implementing a subclass of IDispatch, called ICustomMethods, and registering my C# application:

    public void GetExternal([MarshalAs(UnmanagedType.IDispatch)] out object ppDispatch)
    {
    ppDispatch = this as ICustomMethods;
    }

    From JScript, it just requires calling

    window.external.MyCustomMethod(...);

    So, the problem is that one of these JScript methods I need to support has a JScript array argument, and I don't know how to marshal it.

    Any ideas?

    Thanks much!

    David

  • Anonymous
    April 19, 2005
    A JScript array is a dispatch object which when invoked on its indexes, gets/sets the results.

    In C++ what you'd do to simulate arr[123], for instance, is you'd get the dispid for "123", and invoke on that dispid.

    How you're going to do that in C# beats the heck out of me. We designed JScript arrays years before C# was a gleam in Anders' eye. If you figure something out, let me know.

  • Anonymous
    March 05, 2006
    Something like this works for me


    In Html file's Javascript

    window.external.ArrayReceivingFunction(['Arg1', 'Arg2', 'Arg3',etc.]);


    My C# "window.external" class

    public class WindowExternal
    {
    public void ArrayReceivingFunction(object argArray)
    {
    object[] objArr = DispatchHelpers.GetObjectArrayFrom__COMObjectArray(argArray);
    }
    }


    My C# Dispatch Helpers class

    internal class DispatchHelpers
    {
    internal static object[] GetObjectArrayFrom__COMObjectArray(object comObject)
           {
               int length = Convert.ToInt32(GetPropertyValue(comObject, "length"));
               object[] objArr = new object[length];
               for (int idx = 0; idx < length; idx++)
               {
                   objArr[idx] = GetPropertyValue(comObject, idx.ToString());
               }

               return objArr;
           }

    internal static object GetPropertyValue(object dispObject, string property)
           {
               object propValueRef = null;
               try
               {
                   Type type = dispObject.GetType();
                   propValueRef = type.InvokeMember(property, BindingFlags.GetProperty,
                                                   null, dispObject, null);
               }
               catch (COMException) { /* Throws COMException on invalid property */ }

               return propValueRef;
           }
    }

  • Anonymous
    March 05, 2006
    By the way Eric your info "A JScript array is a dispatch object which when invoked on its indexes, gets/sets the results." was invaluable assistance

  • Anonymous
    April 19, 2006
    The comment has been removed

  • Anonymous
    August 14, 2006
    Playing with jscript here, and wondering if there's a way to get at the KEYS of a jscript associative array from vbscript.  MSE7 seems to know what the keys are, and using For Each, i seem to be able to iterate the VALUES in the array, but I can't seem to hit the keys, though the IDE seems to know they're there.

    Am I out of luck with this one?  I know it's probably a long shot...

  • Anonymous
    August 14, 2006
    You are out of luck.  There is no equivalent to the JScript for-in in VBScript.  Sorry!

  • Anonymous
    January 09, 2007
    Recently I investigated a bug in Jscript which was reported on Vista. The scenario was working perfectly

  • Anonymous
    December 12, 2007
    I have the same problem that David Karlton, but the only difference is that my array has two different dimensions. Here is the example: <script language="javascript" type="text/javascript">      function Array2D(dim1, dim2)      {        for (var i = 0; i < dim1; ++i)        {            this[i] = new Array(dim2);        }        this.length = new Array(dim1, dim2);      } function LoadPage()     {       var mat= null;       mat=new Array(5,2);       var name = '30'; var ar = new Array2D(5,2);        ar[0][1] = "Dato1";        ar[0,1]= 10;        ar[1,0]= "Dato2";        ar[1,1]= 20;        ar[2,0]= "Dato3";        ar[2,1]= 30;        ar[3,0]= "Dato4";        ar[3,1]= 40;        ar[4,0]= "Dato5";        ar[4,1]= 50;        for (i=0;i<=4;i++)        {         ar[i,0]= 'dato'+i;         ar[i,1]= (i+1)*10;        }        if(ar!=null)        {        obj=document.getElementById('TestDll');        mat = obj.LoadPage('30',mat); //Here is the problem } </script> I need to know if is possible to cast the mat array and bidimensional array that that was sent to C# like parameter in LoadPage Function, and How can I do this? I receive an object of type System.__COMObject but I need a type object [,] in C#.

  • Anonymous
    May 05, 2008
    PingBack from http://futureprogramming.com/?p=8

  • Anonymous
    June 04, 2008
    Here's a simple VBScript function that converts single-dimension JScript array to VBArray: <script language="VBScript"> Function toVBArray (ByRef jsa)   Dim e, i, vba()   i = 0   For Each e In jsa          ReDim Preserve vba(i)      vba(i) = e      i = i + 1   Next   toVBArray = vba End Function </script> In fact it can be used on any object, but you will lose property names. It will also skip "gaps" in sparse JScript arrays. You can call it from either JScript or VBscript functions. You can create similar functions for converting more dimensions into arr(1,2,3,...) style arrays by nesting For Each loops - it will require separate function for each given number of dimensions though. arr(1)(2)(3) style VBArrays can be created by modifying this function to call itself recursively (number of dimensions of JScript array would have to be provided as additional argument since there's no way to reliably determine it programmaticaly).

  • Anonymous
    July 02, 2008
    The method from Bim Jim seems good, however I received objects System.__COMObject by reference and I don't know how to get their value (as string for example). Is someone has an idea ?

  • Anonymous
    June 16, 2009
    Adding to agent009 JScript array to VBArray function, I just access JScript arrays using dot notation. x.[0]  'Access the first element of JScript array within VBScript. Works on XP SP3/IE 8 anyways.