IE9 Compat Inspector

With
IE9 now released, we want you to serve IE the same markup as you do for other browsers,
and make sure your site works great running in IE9 standards mode.
We recently blogged about
preparing your site for IE9,
and you can check out the
Internet Explorer 9 Compatibility Cookbook for lists of changes that may impact your site
or the Internet
Explorer 9 Guide for Developers for a more complete list of what’s changed.
Today we are introducing a new resource that can help speed up the process of preparing your site: Compat Inspector.

About Compat Inspector

Compat Inspector is a JavaScript-based testing tool that analyzes your site while it runs.
Compat Inspector reports patterns of interaction which cause issues in standards mode.
This allows you to identify problems quickly without memorizing a bunch of documentation
or searching through the entirety of your site’s code.
We developed Compat Inspector during the course of IE9 to speed up
the process of recognizing common issues across different sites.
Along the way many members of the IE team contributed to the set of test cases
that make up the rules in Compat Inspector. Now we’re making it all available to you.
Check out the
Compat Inspector Test Drive to try it out before using it on your own site.

Compat Inspector is designed to help sites migrating to IE9 Standards Mode,
not those running in legacy modes.
You may still need to refer to the above documentation for some issues.
The best pattern is to use Compat Inspector first,
then fall back to the documentation if nothing is found.

How do I use it?

To use Compat Inspector, add the following script before all other
scripts on each page you want to test:

<script src=”http://ie.microsoft.com/testdrive/HTML5/CompatInspector/inspector.js”></script>

Note: If you have Fiddler,
you can automatically load Compat Inspector on all pages you visit by
adding this snippet
to your
FiddlerScript (which is particularly helpful if your page uses frames).
I recommend installing the
FiddlerScript Editor extension if you don’t already have it.

After you have the above script in place, open your page in IE9 and start using
it. Explicitly test any interactions known to be working incorrectly (only executed
code is analyzed). Compat Inspector will keep a running total of all errors and
warnings associated with detected issues. A summary view in the upper right hand
corner of the page displays the results:

Click on this view to expand it and obtain detailed information about each detected
issue with links to relevant documentation:

Most errors and warnings also provide two additional actions for further investigation:
“Verify” and “Debug.”

“Verify” Workflow

Some test cases have built-in “verifiers” that emulate legacy behavior. This allows
you to confirm the root cause of an issue before making any changes to your code.

Prerequisite: Compat Inspector is opened in the detailed information view
and displaying an error or warning message containing a checkbox labeled “Verify.”

1. Click the “Verify” checkbox for the issue you want to confirm
   
2. Refresh the page (You’ll see a notification that the verifier has been enabled)
   
3. Repeat the steps that originally triggered the error or warning
4. If the issue still occurs
   1. If error or warning messages are still displayed, repeat steps 1-4 for each remaining
      message
   2. Otherwise, Compat Inspector cannot fully identify this issue. Refer to the IE9 documentation
      for additional help.
5. Otherwise, you’ve identified the root cause of the issue
   1. Uncheck all “Verify” checkboxes
      
   2. Refresh the page
   3. Follow the “Debug” Workflow below to locate the source of each message in your code
   4. Follow the instructions in the displayed error/warn messages to resolve the issue
   5. Note: Also look for any “if IE” checks controlling the execution of the problematic
      code. IE9 typically works best when given the same code as other modern browsers.

“Debug” Workflow

Compat Inspector can also help you isolate where in your code things went wrong
via the “debug” feature.

Prerequisite: Compat Inspector is opened in the detailed information view
and displaying an error or warning message containing a checkbox labeled “Debug.”

1. Click the “Debug” checkbox for the issue you want to investigate
   
2. Open the F12 developer tools by pressing the F12 key
   
3. Switch to the “Script” tab
   
4. Click “Start debugging”
   
5. Repeat the steps that originally triggered the error or warning (This will invoke
   the script debugger)
   
6. Switch to the “Call stack” sub-tab located in the right half of the F12 developer
   tools
   
7. Double-click the entry visually below the highlighted entry in the call stack
   
8. Look over at the left hand side of the F12 developer tools to see the code that
   triggered the error or warning
   

How does it work?

Compat Inspector uses features introduced in IE9. At its core, Compat Inspector
overrides native APIs using
ECMAScript 5th edition getters/setters and depends on the browser to correctly
expose APIs per WebIDL. Compat
Inspector then uses these overrides to track interactions between the page and the
native platform. This allows it to report issues at runtime as the problem code
is executed.

The rest of the Compat Inspector infrastructure makes use of various other new features
as needed. Some examples include
DOM Level 3 Core APIs,
DOM Level 3 Events APIs, and
CSS3 Border Radius. Compat Inspector also depends on features introduced
in IE8 such as
HTML5 Local Storage, HTML5
Cross-Document Messaging,
native JSON support, and
Selectors API.

My site works, now what?

Remove the Compat Inspector script from all your pages before publishing. Compat
Inspector is a test tool and should not be used in production. After that, keep an
eye on the IE blog; we may have new test cases to share in the future.

—Tony Ross, Program Manager, Internet Explorer

IEBlog