Can VBScript add properties to objects like JScript?

Question

I am playing with Windows Script Host VBScript and I am curious if VBScript is capable of adding/removing properties like JScript can.

For example:

var global = this;

var test = function() {
    if ('greeting' in global) {
        WScript.echo (
            'global has property named greeting with value: ' + 
            global.greeting + 
            '.'
        );
    } else {
        WScript.echo('global has no property named greeting.');
    }
};

test();
global.greeting = 'Hello, World!';
test();
delete global.greeting;
test();

This code determines the global scope (JScript has no initial access to global scope such as window in browsers or global in Node.js, so I have to find it myself).

The test() function checks if the global object has a key named "greeting", and reports its current state as output.

The code does an initial test to show that global object has no greeting key, then sets the greeting property, then does a second test to show that the greeting key has been added to the global object. After this, the greeting property is deleted and a third test is run to show that the key is no longer a part of the global object.

Is this possible to replicate in VBScript?

I know VBScript has Scripting.Dictionary object that can be used to store such information, but I am curious if there is a way to hook existing objects with new properties and delete such properties in VBScript, or if VBScript has no parallel to JScript's {} construct other than Scripting.Dictionary or Classes (whose properties are immutable).

Ansgar Wiechers Ansgar Wiechers · Accepted Answer · 2016-09-18T20:38:00

Your specific example could be emulated with something like this:

Set global = CreateObject("Scripting.Dictionary")

Sub test
    If global.Exists("greeting") Then
        WScript.Echo "global has property named greeting with value: " & _
            global("greeting") & "."
    Else
        WScript.Echo "global has no property named greeting."
    End If
End Sub

test
global("greeting") = "Hello, World!"
test
global.Remove("greeting")
test

but in general patching objects, or even regular inheritance, is not supported in VBScript. The best you could do to extend a class is wrap it in a class of your own:

Class MyClass
    Private nested_

    Public Sub Class_Initialize
        Set nested_ = CreateObject("Some.Other.Class")
    End Sub

    Public Function Foo(val)          'wrapped method
        Foo = nested_.Foo(val)
    End Sub

    Public Function Bar(val)          'patched method
        x = nested_.Bar(val)
        Bar = x * 42
    End Sub
End Class

Can VBScript add properties to objects like JScript?

1 Answers