In Internet Explorer 8 Beta 2 JScript team has focused on improving developer productivity. You can read 'What’s new in JScript for IE8 Beta 2' and check out the JScript PM Channel 9 video to learn more. As part of our focus on developer productivity we have continued to invest in the IE8 Developer Tools in IE8 and added a JScript Profiler to the developer tools. You can read 'Introducing the IE8 Developer Tools JScript Profiler' for more details on the profiler. The JScript profiler along with the JScript debugger we introduced in Internet Explorer Beta 1 will help you get your site working correctly and optimally.

In this blog I will give more details about the following key improvements we have made in debugger for beta 2, you can check my JScript Debugger in Internet Explorer 8 Beta 1 blog for more details on the features we released in Beta 1:

  • Improved script viewer and script explorer
  • More powerful script console
  • New execution control features
  • Better keyboard navigation and overall usability

One of the goals for the script debugger has been to make sure that debugger has minimal impact on your regular browsing. We made that possible by moving JScript engine to debug mode only when you press start debugging. With this, you no longer need to keep debugging enabled in the Internet Options and thus don’t suffer the performance hit. We also wanted to provide you lot of power even when you are not debugging and ensure that you don’t need to transition to debug mode unless you have to debug. Now with Beta 2 we have added some powerful features to make that possible.

Improvements in Script Viewer

The script viewer in Beta 1 showed all the sources when you are debugging but it only showed source for main page when not debugging. Now with Beta 2 you will be able to browse all the sources even when you are not debugging. You can also set breakpoints even before starting debugging. The breakpoints will persist till you close IE window. To make code easier to read, we have updated the source viewer to show sources in syntax color. This is similar to what you might expect in code editors such as Visual Studio.

Source viewer with syntax colored code

We have also updated the script explorer dropdown to make it easy to browse and select files. Now the script explorer will show the domain to which the script file belongs to. We have also separated the eval code, other dynamic scripts and scripts executed from Console into ‘Others’ submenu of the script explorer. With this change it will be easy for you to find the script file you are looking for.

Source explorer dropdown

Updated Script Console

Console panel in the script tab makes it easy for you to try out new scripts. You can execute the scripts in the console irrespective of whether you are debugging or not. In Beta 2 we have improved the look and feel of the Console so that it is easy to read the output.

To make it easy for you to fix errors on your page, Console also logs all the script errors. These errors will be logged in the Console once Developer Tools has been opened for the tab. You can also navigate to the error location in script by clicking on the error hyperlink in the Console.

To help you log message to Console from your script source we have added support for ‘console’ object. Developer Tools provides multiple level of logging with console.log(),, console.warn(), console.error() and console.assert(). Instead of using window.alert for debugging, you can use these console commands to log messages to the Console. You can call these console commands with a list of arguments that will be concatenated to generate the output string. The input parameters can also be formatted by using substitution patterns in the style of printf().

Console with runtime error and console.log output

You can also control what messages you want to see in the Console pane by using the context menu. Context menu also provide you option to clear the console of all messages. If you only want to clear console.log messages, you can use console.clear().

Context menu for Console

The console.log is extensible and you can add your own console commands through custom scripts. For example you can add console.debug() command which takes string arguments by using following script –

console.debug = function(){

                            var args = "";

                            for(var x=0; x<arguments.length; x++)


                              args += arguments[x];


                            console.log("DEBUG: " + args);


This can be easily enhanced to take formatted strings.

More execution control features

The Developer Tools in Beta 1 offered execution control features like Break All, Step In, Step Out, Step Over. In Beta 2 we have added support for Conditional Breakpoints and Break on Error. In conditional breakpoint you can give any valid JScript expression to be evaluated and debugger will only halt if the expression evaluates to true. Break on Error provides a toggle switch to control whether debugger will break on JScript runtime error or continue while ignoring the error. Regardless of the toggle state the error will be logged to the console so that you can investigate them at your convenience.

We have also extended the just-in-time debugging experience of Internet Explorer. Although with IE8 you don’t need to keep debugging enabled from Internet Options, still if you have debugging enabled in the IE and you hit a script error, you now get an option to use Developer Tools debugger. You can still use Visual Studio and other stand alone debuggers by unselecting the check-box in the message and clicking on Yes.

Just in time debugging dialog

Improved Usability

In Beta 2 we have added extensive keyboard shortcuts. If you have been using Visual Studio for debugging script in IE, you already know the keyboard shortcuts! We have kept the keyboard shortcuts as close to Visual Studio as possible. List of all the keyboard shortcuts supported by JScript Debugger is available here.

We have added search functionality to Developer Tools. Searching in Script tab will show you the search term highlighted in the source viewer. When you browse to a new site or select another file from the source explorer dropdown the search term will continue to be highlighted.

We have also made other improvements like increased tool tips to improve the usability and looks of the debugger.

More Information

For more information on the Developer Tools and JScript Debugger check out these articles:

We look forward to your feedback about the debugger so please leave us a comment in this post. Thanks, and enjoy IE8 Beta 2!

Deepak Jain

Program Manager

JScript Team