XmlMonitor.cls

VERSION 1.0 CLASS
BEGIN
  MultiUse = -1  'True
END
Attribute VB_Name = "XmlMonitor"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

const monitorId as string = "MonitorChannel"

Dim WithEvents parts as CustomXMLParts

Private Sub Class_Initialize()
  Set parts = ActiveWorkbook.CustomXmlParts
  If parts.SelectByNameSpace(monitorId).Count = 0 then
    'create a name space element so that the javascript has something to play with.
    parts.add "<empty xmlns='"& monitorId & "'/>"
  End If
End Sub

private sub parts_PartAfterLoad(ByVal part as CustomXmlPart)
  if part.NameSpaceURI = monitorId then
    MsgBox("msg from officeJS!" & cstr(part.xml))
  end if
end sub

public property Get Channel() As String
  Channel = monitorId
end property