What’s new in F12 with Windows 8.1 Update

We are excited to announce a set of substantial updates to the developer tools in IE, (F12) as well as in Visual Studio 2013 Update 2. The updates in F12 accompany the new releases in IE11.

, we described the capabilities of F12, and its focus on a fast, iterative workflow, on providing accurate data in the DOM Explorer and on providing actionable data in the memory and performance tools.

As you use F12 with this update, you will notice enhancements for the following:

  • A tighter, iterative workflow with change tracking in the CSS tools
  • An ability to debug in the code you wrote such as CoffeeScript or TypeScript, with sourcemaps support, and debug “just-my-code,” if you are using libraries from other developers
  • Enhancements that get you to solutions faster, for example when finding memory leaks, with the enhanced JS snapshot tools and filtering improvements.

Let’s take a look at these improvements to the F12 tools.

Tracking Changes you make in CSS with Change-bars

One of the great strengths of tools like F12 is they allow you to edit the look of any Web site directly within the browser, without you requiring our source code. However, if you spend time making edits it is difficult to keep track of all the changes you make across your CSS and then applying those final edits back to you origin sources. To improve this situation we have introduced an ability to record and track changes, both visually with ‘change-bars’, as well as through a new ‘Changes’ CSS panel in the in the DOM Explorer.

Any change you make in the Styles pane in the DOM Explorer to CSS rules and properties will have a visual clue in the left-margin next to the property or rule that you edited. These are the ‘change-bars’, and they show green for new properties, yellow for changed properties and values and red for deleted properties. These change-bars will be retained, even if you begin to look at other DOM nodes.

Changebars on the styles tab

Changebars on the Styles tab

As you may make multiple edits across many nodes, we added a new tab in the CSS panel that lists all the changes in the current F12 session, as a ‘diff’ view so that you can use it as a checklist when you make manual edits to your source code. It also supports the ability to copy and revert changes through a context menu.

The new changes tab

The new Changes tab

Debugging your App with “Just My Code”

If you are developing Web sites and apps, then you are likely using 3rd party libraries like jQuery or Angular, and typically these libraries are often minified. We often see developers who are debugging their code step into library code, and get buried in the depths of that library, before being able to get back to their code to debug their issue.

Visual Studio has supported a feature called “Just My Code” (JMC) managed languages for a while and with Visual Studio 2012, it is also enabled for JavaScript. The idea behind JMC is that we keep the debugger in your code, in the code you want to debug and not into code you can’t really change.

With this feature now in F12, there are two key things you will see when you debug

  • You will never ‘step into’ a file (library) that is marked as library code. You can mark a library through the file picker in the debugger (see below), even if you have stepped into the file. Once marked, any step operation will take you to your code.
  • If you enable “break on all exceptions” you will never break on an exception thrown and handled in library code.

Marking files as library code

Marking files as library code

By default F12 will recognize files that match the URL *.min.js as library code. You can modify this behavior easily however, by marking libraries in the debugger’s file picker or in the context menu of the file tab if you have the file open in the debugger.

We will show much more about this feature and the workflow in a follow-on blog post.

Debugging your App written with other Languages using Source Maps (v3)

As JavaScript apps have become more and more complex recently there’s an increasing trend to author in another language that compiles to JavaScript (the F12 tools are written in TypeScript and compiled to JavaScript for example). Similarly, you may have minified JavaScript code that is not the origin source that you wrote the app in. This compilation process means the JavaScript that executes in the browser and that you debug, isn’t the code you have in your editor, which makes debugging more challenging.

To solve this problem, there’s a community-driven format that has gained a lot of traction with browsers and Visual Studio, that maps origin source and compiled files called “Source Maps” (spec). These maps are generated during compilation and with this release of F12 we’ve added support for v3 of the Source Map spec.

When a compiled JavaScript file defines a valid source map, F12 will default to load the original source file, rather than the running JS file, when ‘source maps’ are turned on (a button on the debugger). You will have the following capabilities:

  • Files in the file picker use their origin source name, rather than the running documents.
  • The file(s) you open in the debugger, and use to step through your code are your origin source files, and for TypeScript, CoffeeScript and Script # these files will be colorized appropriately (as you can see with the TypeScript file below).

The file(s) you open in the debugger, and use to step through your code are your origin source files, and for TypeScript, CoffeeScript and Script # these files will be colorized appropriately

As with Just-My-Code, we will go into more depth on source maps in a follow-on blog post.

Three way snapshots

When debugging a memory leak, you typically will be presented with a large amount of data, even if filtered) that memory profilers create, which makes finding that leak complicated. In F12 we had previously taken steps for the tools to summarize the state of the app in the snapshot tiles, and opportunistically suggest potential issues with the detached DOM information indicators. However, in this update, we wanted to take this further, by helping developers zero-down on issues even easier.

The F12 Memory tool now includes the ability to compare three snapshots (and get a scoping view of those snapshots), that is a cleaner process to determine a leak. The snapshots are:

  • The initial state of your app before you start the scenario that provides the baseline for objects in your app.
  • Once your scenario is completed, which may augment the possible baseline for your app, which then requires a further snapshot once you execute the scenario again.
  • The ‘back to normal’ state of your application, once you try the scenario again. In this state all of the objects from your scenario should have been freed (or you expect them to be alive).

With these snapshots you can compare them and use the new “Scope” filter dropdown to select the “objects left over from snapshot #2,” which represents your scenario end state and potentially a set of objects that shouldn’t be around anymore, as shown below.

Scope filter

Scope filter

The types view that you see above, shows the list of objects and a gutter indicator of where potential issues may reside.

Tooling for IE on Windows Phone in Visual Studio 2013 Update 2

If you have spent time trying to make a compelling mobile version of your Web site you have likely hit issues with it not looking or working correctly on mobile browsers.  To help with this on Windows Phone, we’re excited to announce that in Visual Studio 2013 Update 2 we have enabled the use of Visual Studio’s debugging and performance tools for Internet Explorer on Windows Phone 8.1. For more details on this have a read of the Visual Studio ALM Blog on this topic.

Many other improvements…

In this release of F12 we’ve tried to address many customer requests, as well as address bugs that include several crashes caused by the network inspector and not respecting conditional comments when using F12 to emulator lower document modes. Rather than the list the bugs here the bugs will be updated on the Microsoft Connect site for IE (https://connect.microsoft.com/IE/Feedback).

Here’s a more detailed list of the changes you’ll see in this release of F12.


  • Ctrl+[ and ctrl+] to navigate between tools


  • Dropdown to enumerate execution targets.
  • Inspect objects that are logged via console.log including printf-style formatting.
  • Locals (at breakpoint) in intellisense for the console.
  • Console $_ shortcut to access the result of the last evaluation in the console.
  • Always record console messages – before F12 launch (via Internet Options -> Advanced -> (check) Always record developer console messages).


  • Persist BPs, Watches, Tabs and the like so I don't keep losing my state.
  • Debug my Typescript/compiled code inside F12 using Source Maps.
  • Debug just my code and not be bothered by library code (JMC).
  • Name eval code via //#sourceUrl=<url> comment.
  • Keyboard shortcut to abort and refresh page when broken via ctrl+shift+f5.
  • Fully qualified function names (e.g. a.b.c) in call stack and profiler views.

DOM Explorer

  • CSS pseudo states - set the pseudo state for an element to test out my pseudo styles.
  • CSS Changebars - see what values have changed in the styles view.
  • CSS Changes View - see final applied CSS changes and copy to clipboard.
  • Combined Computed Style Panel - view the CSS styles in a cohesive and CSS pane adding editing and links to source.
  • Ctrl+b in DOM Explorer for select element.


  • Doc Mode Awareness - why my page is in certain doc mode in order to understand my compatibility scenarios better.

UI Responsiveness

  • Sort all levels of events in the timeline details view by duration.
  • Simplify the timeline details view by filtering out events within certain categories (e.g. GC, Image decoding).
  • Easily zoom the graph and detail views to the duration of time for a specific event instance (via context menu).
  • Identify the exact property that was changed (and the value it was changed to) when a DOM element's inline styles are programmatically modified.


  • Identify the line of code that was responsible for allocating a specific function, so that I can correlate memory with source.
  • Context menu item to show object in dominators view (and view retained size etc.).
  • Updates to the types views to show which type(s) accounted for the majority growth in a diff, so that you can rationalize object churn more easily.
  • Gridlines on table UI.
  • Settings UI (show built ins, circular refs, object ids).


With this update to IE11 and F12, we’re updating developer tools more often getting you the latest features and bug fixes as soon as we can. Expect to see and hear from us more and if you’d like to provide feedback, or ask for new features and help simply reach out on twitter @IEDevChat, or through the IE11 Send Feedback tool or on Connect.

This post just scratches the surface of what’s new in F12. Over the next few weeks we’ll be publishing blog entries that go into more depth and show you how to use F12. There’s also our complete F12 developer tools documentation on MSDN.

In the meantime, we look forward to your feedback. You can reach out to the team on Twitter @IEDevChat, through the IE11 Send Feedback tool or on Connect.

— Andy Sterland, Program Manager, F12 Tools

— Jonathan Carter, Program Manager, F12 Tools

— Simon Calvert, Lead Program Manager, F12 Tools

Comments (36)
  1. The Deeds says:

    Thanks for the tremendous updates!

    Here is my feedback:

    – Still we can't select multiple rules in CSS view. no ruler and color picker.

    – Also, when the F12 windows is focused, pressing F5 has no effect: expected behavior is to refresh the corresponding page.

    – Copy with styles doesn't copy @font-face declaration.

    – Cannot paste multiple CSS rules (like Chrome).

    – Cannot quick edit HTML tag name.

    – VS-like color pallet missing in CSS/HTML views.

    Here are the corresponding connect reports:

    798046 F12 developer tools: Visual Studio 2012+ like priority color palette

    791981: F12 developer tools: Cannot select and paste multiple CSS rules and properties.

    [Fixed] 792543: F12 developer tools: CSS rule copies with 3 space indentation instead of 4.

    797447: F12 developer tools: "Copy elements with styles" ignores @font-face.

    798009: F12 developer tools: quick glance at elements' dimensions (height, width, border-radius) and images preview.

    798021: F12 developer tools: Color picker and Ruler tools.

    [Fixed] 800084: F12 developer tools: tools: Ability to toggle element states.

    [Partially Fixed, Reason="IE refreshes the page"] 801923: F12 developer tools: media query overrides for debugging layout.

    805145: F12 developer tools: Ability to quick edit start-tag and its corresponding end-tag.

    805163: F12 developer tools: Change numeric values using keyboard up/down keys.

    811024: F12 developer tools: Disconnected with browser window.

  2. Arieta says:

    The hangup issues indeed seem to be fixed. Very nice. I hope we can see upgrades like this one more often…

    An ability to copy the URL / jump to the URL specified in the Background CSS tag would come very handy.

  3. Den says:

    But, guys I cannot even download the update for my Win 8.1. What is the delay? Are UK users treated differently?

  4. ididit says:

    Thanks for the update.

    Hitting F12, with attached Debugger(2013RC2), will changeover to VS.

    Is this purposed?

    I had to press F5(in IE) first and F12 to avoid this.

    F12 is even stable now on Win7, thanks again.

  5. RichB says:

    JustMyCode – I've been longing for this for some time. Thankyou!

  6. ZippyV says:

    I'm still missing a CSS tab like in the previous F12 tools. Other than that it's almost at the same level as the other browsers' developer tools.

  7. The Deeds says:

    Guys if you can reproduce the following issue on other sites, please vote (click on "I can too"):


  8. Now you're talking, IE team!

    Maybe if you keep up the good work, IE would become the best web browser once again.

  9. AndySterland says:

    @The Deeds – Thanks for all the feedback, for each item you mentioned:

    Color picker – This is on our backlog but isn't near the top

    Ruler – This is on our backlog but isn't near the top

    font-face – Working with font-face and keyframes and the like is a feature that's high on our backlog

    F5 – The F5 key when focused in F12 is meant to 'continue' which only works when broken in the debugger, we don't intend on overloading this key usage with refresh for the page. If your focus is on F12 you can press F12 to focus on IE and then F5 to refresh. If you're pinned this will hide F12 if you're unpinned it will just change focus.

    multiple select in styles – This is on our backlog near the top

    Edit tag name – I've added an item to our backlog for this, you can do it via edit as HTML today but as you call out there isn't an easier mechanism.

    @Arieta – Thanks for the feedback, I've added a note to a feature on our backlog for previewing/opening URLs wherever we show them.

    @ididit – VS will attach the script debugger as well as launching the DOM Explorer and the console in Visual Studio (we ship the same tools in F12). The F12 key then brings VS to focus when you hit. In general the F12 key is used to bring up the tools and if you attach with VS the tool is VS as both F12 and VS can't be debugging the same page at the same time. Also if you hit F12 while on F12 we should bring IE into focus.

    @ZippyV – Adding a CSS view to the tools is on our backlog, and near the top, I've +1 the feature.

  10. Slawek says:

    Please provide the resources explorer like in chrome in order to debug cookies, local storage, session storage and indexeddb

  11. MgSm88 says:

    Is this available for Win7 currently? I don't see any information on that or a place to download the update.

  12. Bryan says:

    So am I correct in understanding that IE Conditional Tags will now register correctly in IE11? I feel like if this is so, it should be made very clear that this now works, as this was the main reason I REVERTED back to IE10.

  13. Andy Sterland says:

    @slawek – Thanks for the feedback, resource views for cookies, local & session storage, and indexedDb are all on the backlog. Though cookies and storage are higher up than indexedDb.

    @MgSm88 – The update is distributed via Windows Update and should be available for download.

    @Bryan – Yes conditional comments should work when using F12 to change document modes. Conditional comments were always supported in document modes < IE10 (they were removed in IE10 msdn.microsoft.com/…/hh801214(v=vs.85).aspx) just not when set via F12 :(.

  14. Paul says:

    That was a huge amount of improvements, awesome!

    BTW, are there ways to not break into scroll/timer events when I click the little pause icon? I want to find what code is run when I mouse over something without knowing where to set the breakpoint.

  15. CvP says:

    I just wanted to let you know I'm extremely happy with the amount of F12 dev tools improvement and the way it is heading.

    Can we please get some love for the CSS?

    The CSS tab went missing and there is no "pretty print" for css. We need list of CSS files, pretty print and the ability to edit those files from F12 tools on the fly.

  16. Surya says:

    Still no conditional comment support for older browser modes?  That still makes that function unuseable.

    If you don't want people to use that function for checking and debugging, why include it at all?

  17. Michael says:

    Hi, IE Team – You broke o365!

    The compatiblity mode in IE11 after Update 1 is no longer active on SharePoint Online sites. It breakes the functionallity for ordinary users using the newest IE (for example editing webparts)

  18. PaulUs says:

    I still don't like the tabs being vertical, my most commonly used are at opposite ends and it really slows down debugging. Can't we have them horizontal again like debuggers in all other browsers? Or at least an option to switch.

    Pretty please? 🙂

  19. Jake says:

    @Paulus, please post Connect link so I can vote for this suggestion. Wait, you didn't reported on Connect yet? Go ahead and do the right thing. Help yourself !!!

  20. Louis says:

    Is this problem now fixed?


    If yes, is this only for Win8 users?

  21. Feng says:

    I wish 'Disable' menu can be added back, so we can easily disable script, css, etc. I also like to see improvements in Console that allows to print out function definition without using .toString()

  22. Feng says:

    add more options in emulation similar what Chrome does, so it's friendly for mobile developers

  23. VebDev says:

    F12 is great however if IE completely freezes how would you debug the issue. I am having a problem in my current website where i am using multiple javascript plugins and something in those plugins makes IE9 completely freeze. Same code works fine in higher versions of IE.

  24. Niki says:

    @AndySterland – can you please post what is on backlog

  25. Real McCoy says:

    I second Niki.

    Guys please open up with us. We are only here to make IE better for humanity.

    Please open a uservoice channel and see how most people feel. Don't trust corporations too much, this is the main reason why IE is where it is and other browsers are getting better rather quickly.

    Let us share the ideas in rather expressive and interactive manner. Something like http://www.conceptshare.com/


    @AndySterland, thanks for your patience. I have two requests about the shortcuts. The following works in all major non-IE browsers:


    Missing shortcut in IE:

    While holding the Ctrl button, if you press browser's back or forward button it should open the corresponding (previous or next) page in new tab. This behavior is present in Firefox, Chrome and Safari.

    Incomplete implementation in IE:

    While holding the Ctrl button if you press 0 (zero) on qwerty keyboard, the zoomed page is reverted to normal. But if the 0 is pressed on num-pad, the shortcut doesn't work.


    I submitted the bug report in 2011: connect.microsoft.com/…/one-missing-and-another-poorly-implemented-shortcut. Please +1 this too.

    Thanks in anticipation.

  26. Real McCoy says:

    One more thing; please add "Paste and Go" in address bar's context menu. IE11 modern desktop has it but its missing from desktop version connect.microsoft.com/…/paste-go-absent-in-desktop-internet-explorer

  27. Martijn says:

    So you're not fixing the IE8 emulation mode? Because it breaks certain websites catastrophically, and it doesn't work at all for quick testing.

    The reason: conditional comments in IE8-mode are parsed (read: ignored) as if the browser was still in IE11/edge mode.

    Please fix this. NOT ONLY IN IE12, BUT IN IE11.

  28. Martijn says:

    @Real McCoy

    Yes, that, and Reading View as well. I see no reason why IE would only allow that in the Metro layout. Becasue of that, Windows 7 and Windows 8 desktop folks are missing this feature entirely.

  29. __hAl__ says:

    IE11 for Windows Phone 8.1 is crashing much more easily than the desktop version of this browser.

    That is a bad regression.

  30. Cortana says:


    This is a bad bug report chief!

    In this case; what are the steps of reproducing this issue? Have you filed a bug report on Connect (link please)? If you don't have time or don't want to report it properly, please don't brag about it improperly.

    Since things have changed @Microsoft and I (Cortana) am looking after your issues too. Thereby, I would highly suggest you to regain trust on IE's Connect channel and make a bug report for each issue you face in IE. IE team will respond to those!

    Sounds good? Or would you like me to remind you at some point?

  31. Sam Hasler says:

    "always record developer console messages" appears to be buggy. With it turned on I am seeing what look like "replays" of console messages for old version of a js file, not the behaviour I'd expect after the changes I've made. I've also seen console messages appearing out-of-order.

  32. Jim says:

    @Sam Hasler, please report this issue at connect.microsoft.com/IE and send us the link so we can vote it. Thanks.

  33. joann keith says:

    THANKS for the info!  JOANN

  34. Andy Sterland says:

    @paul Thanks! There isn't a way to break on specific events such as mouseover. It's something we are working on now.

    @Riasat Thanks! Improving our CSS feature is high on our backlog for sure and something we know that needs to improve.

    @Surya when emulating older document modes from F12 you should see conditional comments work as expected.

    @Michael I've passed your comment on to the compat team.

    @louis yes it should be fixed for all IE11 Update 1 users.

    @feng improving our emulation tool is something we'd sure like to do, did you have any specific needs?

    @niki and @Real McCoy We're working on figuring out how to post our backlog and if it should be part of status.modern.ie or something else so hopefully we will be able too.

    @Martjin The issue of ignoring conditional comments should be fixed now. But keep in mind that IE11 emulating IE8 isn't a perfect solution.

    @Sam Hasler There was a bug that shipped in update 1 where you received duplicate console messages, we will fix it in the next update.

  35. John Jansen [MSFT] says:

    @Michael, can you elaborate? It should be working, so I'll need to investigate. What SharePoint URL are you hitting?

  36. Internet Exploder says:


    Enjoy your remote exploits.

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