define('DISALLOW_FILE_EDIT', true); November 2009 – unFocus Projects – Kevin Newman and Ken Newman

Trace Actionscript in a Browser

Testing Flash apps in a browser can be cumbersome, but it needs to be done for some browser only functionality, such as deep linking and back button functionality – as well as checking other things that might change once you are out of the Flash “test movie” sandbox, and into the browser – things like file path issues. The convenient trace window is not available in the browser, but there are alternatives.

Flash Content Debugger and “Allow Debugging”

While it’s not essential for tracing, the first thing you should do, is make sure you are running a content debugger version of the Flash Player. You need both the Active X version for IE, and the Plugin version for everyone else (Firefox, Chrome, Opera, Safari, etc.). Both plugin types have their quirks with regards to JavaScript (and other platform differences), and really require specific testing in each, so make sure you grab both versions. Once you have those, you’ll be able to see uncaught exceptions in AS3 swfs right in the browser. You can even use the Flash Content Debugger from the browser, though I haven’t found a smooth way to do that yet. For many thing, a simple trace is all you need.

A quick tip that took me a while to notice – the “Allow Debugging” checkbox in Flash’s Publishing Settings dialog, actually causes the Flash compiler to add debugging symbols to the compiled swf, symbols that give you useful information like the actual line number of an error, in addition to the stack trace. The “Allow Debugging” verbiage, is most definately not enough to communicate that difference – I thought it was more of a locking mechanism. Hopefully you haven’t stumbled around for too long with that, like I did when I first switched to AS3..


The easiest way to trace from Flash is to use Firefox with the FlashTracer extension from With FlashTracer, you can use the regular old built in trace method without any extra work on your part. Make sure you download the one from (2.3.1), since the one from (2.2.0) doesn’t work in Firefox 3.5. For many things that’ll be all you need. But sometimes, you’ll need information in other browsers, and will want to trace to the browsers JavaScript console. In addition to simple trace messages, you can also call a number of other methods that will out put your messages in different formats and colors, making it easier to spot what you might be looking for.

Check out the Firebug Console API for more information.

Enabling the JavaScript console

If you are already familiar with the various JavaScript consoles, please feel free to skip to this part.

Each of the major browser vendors has a JavaScript console implementation, and thankfully, the API is mostly compatible with one another. The GUI is a bit different in each (except Safari and Chrome – both are based on WebKit), so here’s a quick rundown on how to access the JavaScript console for each:


You should get to know and love Firebug. It is currently the best developer tool available on any platform – so good the others all copied it, even if they won’t admit it (*cough*Microsoft*cough*). Firefox is oddly enough, the only browser that doesn’t ship with a JavaScript console, and requires you to install an extension. While running Firefox, you can find and install that extension at

Once Firebug is installed, you will notice a little bug (insect) icon in the bottom right hand corner of the browser window, on the status bar. Click that to open and enable Firebug for the page you are currently viewing. Firebug will only turn itself on, on a site by site basis, and only after you click on that bug icon. Once it has popped open, you will see some tabs, with many goodies like the fabulous “Net” tab (very useful to make sure swfs are being loaded in the browser), and the “HTML” tab, which contains a live, nested version of your html code, which can be edited in real time – it’s hard to describe how much better life is in the Web Development since Firebug. Anyway, the tab we are interested in, is the “Console” tab – click that. On the actual tab, there will be a little down arrow – click that to open a menu, then click “Enabled” to turn the console on (the onscreen instructions are a little odd, their picture is of the “Script” tab – the arrow you want is on the “Console” tab, not the “Script” tab).

Internet Explorer

You’ll need to upgrade to IE8. If you are stuck on IE6, I’m sorry for you. You will not be able to easily debug Flash apps – that browser is simply difficult to work with, and you’ll probably need to output to either a text field within flash, or to a div element using JavaScript. Go and download IE8 now, if you don’t already have it. Once you have IE8 installed, you can find the “Developer Tools” under “Tools” menu. You can also press F12 to bring them up. The dev tools in IE8 are docked to the main window, along the bottom of the screen, very much like Firebug. You will notice 4 tabs in a blue bar, below a row of link buttons – click the “Script” tab to open the script tools. You will have two panes at that point – in the left is a debugger, and in the right pane, you should see a button for the Console.


You’ll need to enable the developer tool first, before you can turn on the JavaScript console. Click on the gears icon on the main toolbar, and choose “Preferences”, then click the “Advanced” tab (the one with the gear icon). On that page, there is a checkbox labeled “Show develop menu in menu bar”. Check that, and close the window. Now under the Page icon menu, you’ll see a sub menu called “Develop”. In that sub-menu, choose “Show Error Console”. This will open the “Web Inspector” window. You can dock the window along the bottom of the main window by clicking the dock button in the bottom left of the Web Inspector window. To the right of that button, there is another button with a greater than sign, and three lines. That button will toggle the JavaScript console.


Click the page drop down icon on the right of the main toolbar to open the main menu, then go to Developer, then JavaScript console. This will open the “Developer Tools” window, which contains the many things, including the JavaScript console. You can dock window inside of the main window by pressing the dock button on the bottom left of the popup window. To the right of that button, there is another button with a greater than sign, and three lines. That button will toggle the JavaScript console for Chrome.


Under the Tools menu, choose the “Advanced” submenu, then choose “Developer Tools”. This will open a panel along the bottom of the main window (sensing a trend here?). In that panel, click on the “Error Console” tab. If you’d like to only see JavaScript errors, you can click the bottom JavaScirpt tab (under the white output area of the Error Console). Note: Their is an alternative “Error Console” under Tools -> Advanced -> Error Console. Try them both, and use the one you prefer.

Tracing to the Console

Once you have familiarized yourself with the JavaScript console, you can start to trace to it. The JavaScript command is simple enough:

[cc lang=’javascript’ ]
window.console.log(“your message”).

From Actionscript you’ll need something like this:

[cc lang=’actionscript’ ]
import flash.external.ExternalInterface;“console.log”, “your message”);

Since we are using ExternalInterface, you’ll need to make sure you have the allowScriptAccess object param, or embed attribute set to an appropriate value – either “always” or “sameDomain” (sameDomain is the default, so as long as you have your html/javascript/swf all on the same domain, you should be good to go).

You should now be able to trace (or something like it) in the browser. Next time I’ll cover some more advanced uses, as well as some more specific snafus with deep linking and browser back button functionality.