DukTape JS

Author: Dave
Date: 06.05.15 - 7:38pm

I have been tinkering with a new project, to try and get the dukTape js engine working with visual basic six. My end goal hopefully would be similar to what I did with script basic.

Since JavaScript supports obj.method notation, this time around I want to up the ante and be able to call methods on com objects the same way you can in the Microsoft script control.

So how do we map an arbitrary number and prototypes of functions and wire them into the correct method on the COM object.

When you call AddObject in the Microsoft script control, it has to use the typelib information to extract all of the prototypes to know how to call them. Ok I have done this.

But how do you create the necessary JavaScript prototypes and wire them all up to send them to the correct com method?

in the duktape C api you can create arbitrary objects and methods on them..but they are designed to each call a specific C function. This wont work for what I am trying.

Here is what I came up with so far. it is working, but will be further refined.

I added a single native C function called resolver.

int comResolver(duk_context *ctx) {
	int i, retType ;
	const char* meth = 0;

	int n = duk_get_top(ctx);  /* #args */

	if(n < 0) return 0;
	if(vbHostResolver==NULL) return 0; 
	meth = duk_safe_to_string(ctx, 0); //first arg is obj.method string
	retType = vbHostResolver(meth, strlen(meth), ctx, n-1);

	return 1;  

then i built up a javascript class source file (manually for now)

function dlgClass(){
	this.ShowOpen = function(filt,initDir,title,hwnd){ 
		return resolver("call:cmndlg:OpenDialog:long:[string]:[string]:[long]:r_string", filt,initDir,title,hwnd); 

function fsoClass(){
	this.ReadFile = function(fname){
		return resolver("call:fso:ReadFile:string:r_string", fname); 	

var cmndlg = new dlgClass();
var fso = new fsoClass();

var form = {
  set caption (str) {
    resolver("let:form:caption:string", str); 
  get caption() {
    return resolver("get:form:caption:string"); 
  ReadFile : function(fname){
		return resolver("call:fso:ReadFile:string:r_string", fname); 	
  ShowOpen : function(filt,initDir,title,hwnd){ 
		return resolver("call:cmndlg:OpenDialog:long:[string]:[string]:[long]:r_string", filt,initDir,title,hwnd); 


Now in vb6 I can do the following (all testing and working so far) to make alert() work I rewired the DUK_FWRITE to redirect to my own stdout handler which calls back to vb6

rv = Eval("1+2") 'works
rv = Eval("alert(1+2)") 'works
rv = Eval("pth = cmndlg.ShowOpen(4,'title','c:\',0); alert(fso.ReadFile(pth))") 'works
rv = Eval("form.caption = 'test!'; alert(form.ReadFile('c:\lastGraph.txt'));")
rv = Eval("form.caption = 'test!';alert(form.caption)")

So everything is looking good so far. property gets and sets are functional as are arbitrary method calls. To make the magic work my vb host resolver function
  1. looks up the live object from the name
  2. extracts method/property name
  3. loads a variant array with the relevant args/values/types
  4. uses TLIApplication.InvokeHook to call the method
  5. sets the return value
  6. returns execution back to the script.
So with the initial experimentation stage up and running, next step will be to use the typelib info to parse the COM objects on the fly when I call AddObject and build the appropriate js class file for each, and well as save the method info for the resolver.

I will probably save the method info in a class in parsed format and just use a methodID in the javascript file instead of a full text based prototype which is bulky but good for initial testing.

Before I goto much farther down that road which will be a lot of work though..I think I will start experimenting with the debugger capabilities (here and here) to make sure I can control it.

just having a more modern Javascript implementation available for VB6 is already a win, COM object support was a must have though. but if I can build a full IDE for it like i did for script basic..then that will knock it out of the park.

One more thing to resolve..right now all the COM objects and methods I have tested are on static global top level objects. What if a method returns a new object instance such as with the Microsoft Scripting runtime or Excel automation? ex:

Function OpenTextFile(FileName As String, 
	[IOMode As IOMode = ForReading], 
	[Create As Boolean = False], 
	[Format As Tristate = TristateFalse]
) As TextStream

Function ReadAll() As String Member of Scripting.TextStream

how to call a method on a specific instance of an object instead of static top level global objects like we have been? My first thought was to add a int field to the TextStreamClass of my own that would hold an objptr(obj) to identify it uniquely. Resolver will have to return a new class instance, and set say a hInst field of it. Thanks to some help from the guys on the IRC channel this is already working in a simple test scenario ex:

duk_get_global_string(ctx, "fsoClass"); 
duk_new(ctx, 0);

Also looking at the debugger docs, they are marked as highly experimental. My instinct is telling me to hold off on messing with the debugger side of it for a bit just in case.

Comments: (0)

Leave Comment:
Email: (not shown)
Message: (Required)
Math Question: 98 + 73 = ? followed by the letter: C 

About Me
More Blogs
Main Site
Console tricks
FireFox temp dir
OCX License
Extract substring
VB6 Console Apps
VB6 Debugger View As Hex tooltips
VB6 - C Share registry data
VB6 Addin Missing Menus
VB6 Class Init Params
VB6 isIn function
Python and VB6
Python pros and cons
download web Dir
vc rand in python
VB6 Language Enhancement
Register .NET as COM
UDT Tricks pt2
Remote Data Extraction
Collection Extender
VB6 FindResource
DirList Single Click
Reset CheckPoint VPN Policy
VB6 BSTR Oddities Explained
SafeArrays in C
BSTR and Variant in C++
Property let optional args
Misc Libs
Enum Named Pipes
Vb6 Collection in C++
VB6 Overloaded Methods
VB6 Syncronous Socket
Simple IPC
VB6 Auto Resize Form Elements
Mach3 Automation
Exit For in While
C# self register ocx
VB6 Class Method Pointers
JS Debugger
Duktape Debug Protocol
QtScript 4 VB
Vb6 Named Args
vb6 Addin Part 2
VB6 Addin vrs Toolbars
OpenFile Dialog MultiSelect
Duktape Example
DukTape JS
VB6 Unsigned
.Net version
TitleBar Height
.NET again
VB6 Self Register OCXs
Query Last 12 Mos
Progid from Interface ID
VB6 to C Array Examples
Human Readable Variant Type
ScriptBasic COM Integration
CodeView Addin
ScriptBasic - Part 2
Script Env
printf override
History Combo
Disable IE
API Hooking in VB6
Addin Hook Events
FastBuild Addin
VB6 MemoryWindow
Link C Obj Files into VB6
Vb6 Standard Dlls
CStr for Pascal
Lazarus Review
asprintf for VS
VB6 GlobalMultiUse
Scintilla in VB6
Dynamic Highlight
WinVerifyTrust, CryptMsgGetParam VB6
MS GLEE Graphing
printf for VB6
C# App Config
Tero DES C# Test
VC 2008 Bit Fields
Speed trap
C# Db Class Generator
VB6 vrs .NET (again)
FireFox Whois Extension
git and vb6
Code Additions
Compiled date to string
C# ListView Sorter
VB6 Wish List
C# Process Injection
C# PE Offset Calculator
VB6 Async Download
Show Desktop
coding philosophy
Code release
Dll Not Found in IDE
Advanced MSScript Control
random tip
Clipart / Vector Art
VB6 Callback from C#
Binary data from VB6 to C#
CSharp and MsScriptControl
HexDumper functions
Js Beautify From VB6 or C#
vb6 FormPos
Inline Asm w VB6
The .NET Fiasco
One rub on computers
Universal extractor