When I am developing new script, I usually use VBScript (or powershell but that’s another story).

but sometimes I already have some old functions written in JScript, that I need to use in my VBScript.

This is often if I am creating a HTA.

This code example shows how to use both languages in HTA:

<script language="VBScript">
  Sub vbMessage()
    ' Here's a client-side VBScript.  It will display a message box.
    MsgBox "This message box was called from a VBScript function."
  End Sub

<script language="JavaScript" type="text/javascript">
  function jsMessage()
    /* This is client-side javascript.  It will display a message box. */
    alert('This message box was called from a Javascript function.');
    /* Now see if we can call a VBScript function... */
    vbMessage() ;

<form name="frmTest">
  <input type="button" value="Test Two Scripts!" onclick="javascript:jsMessage();" />

Notice that the onclick on the button does not call

onclick = “jsMessage();”

but instead we call it by

onclick = “javascript:jsMessage();”

This tells the script to use the js function instead of the vbscript function.

therefore you have full control, even if both VBscript and JScript contains a function by the same name.