How to debug an MSI Custom Action that is implemented in Javascript? - wix

Question

I'm having difficulty figuring out why my Javascript Custom action is failing.
I thought I saw a topic in the WIX.chm file on debugging; now I cannot find it.
Q1
is there doc on how to debug Javascript or VBScript custom actions?
Q2
Is there a way to emit something into the MSI log from a custom action?
Addendum:
Some people think script is the wrong tool for writing CAs.
I don't agree. I think Javascript is a very good tool for the job.

Answer 1

For the doc, look for Session.Message.
To emit messages into the MSI log from a Javascript Custom Action, follow this boilerplate code:
//
// CustomActions.js
//
// Template for WIX Custom Actions written in Javascript.
//
//
// Mon, 23 Nov 2009 10:54
//
// ===================================================================
// http://msdn.microsoft.com/en-us/library/sfw6660x(VS.85).aspx
var Buttons = {
OkOnly : 0,
OkCancel : 1,
AbortRetryIgnore : 2,
YesNoCancel : 3
};
var Icons = {
Critical : 16,
Question : 32,
Exclamation : 48,
Information : 64
};
var MsgKind = {
Error : 0x01000000,
Warning : 0x02000000,
User : 0x03000000,
Log : 0x04000000
};
// http://msdn.microsoft.com/en-us/library/aa371254(VS.85).aspx
var MsiActionStatus = {
None : 0,
Ok : 1, // success
Cancel : 2,
Abort : 3,
Retry : 4, // aka suspend?
Ignore : 5 // skip remaining actions; this is not an error.
};
function MyCustomActionInJavascript() {
try {
LogMessage("Hello from MyCustomActionInJavascript");
// ...do work here...
LogMessage("Goodbye from MyCustomActionInJavascript");
}
catch (exc1) {
Session.Property("CA_EXCEPTION") = exc1.message ;
LogException(exc1);
return MsiActionStatus.Abort;
}
return MsiActionStatus.Ok;
}
// Pop a message box. also spool a message into the MSI log, if it is enabled.
function LogException(exc) {
var record = Session.Installer.CreateRecord(0);
record.StringData(0) = "CustomAction: Exception: 0x" + decimalToHexString(exc.number) + " : " + exc.message;
Session.Message(MsgKind.Error + Icons.Critical + Buttons.btnOkOnly, record);
}
// spool an informational message into the MSI log, if it is enabled.
function LogMessage(msg) {
var record = Session.Installer.CreateRecord(0);
record.StringData(0) = "CustomAction:: " + msg;
Session.Message(MsgKind.Log, record);
}
// popup a msgbox
function AlertUser(msg) {
var record = Session.Installer.CreateRecord(0);
record.StringData(0) = msg;
Session.Message(MsgKind.User + Icons.Information + Buttons.btnOkOnly, record);
}
// Format a number as hex. Quantities over 7ffffff will be displayed properly.
function decimalToHexString(number) {
if (number < 0)
number = 0xFFFFFFFF + number + 1;
return number.toString(16).toUpperCase();
}