F12 The best kept web debugging secret

Article
10/18/2011

Shhh don’t tell anyone about this blog, then you will look brilliant in front of your co-workers when you show them these cool tools! Have you found the F12 key yet in Internet Explorer? I will admit that until 6 months ago I hadn’t. If you are running Internet Explorer 8 or 9 you can try it right now. Just hit the F12 key and a window appears at the bottom of your screen. This window will help you debug your web pages! No external tools or plug-ins required! The developer tools were available in IE8, but there were some new features added in IE9, so if you haven’t done so yet, download IE9 so you get the every last bit (and byte!)

The developer tools give you six different tabs to help you debug and walk through the code on your web site.

Tab	Description
HTML	Your tab for checking out the HTML on the web page with the options you would expect, for clearing the cache and refreshing the page.
CSS	This tab allows you to examine each of the CSS files used to style your page. You can even deselect different CSS style settings to see how it affects the appearance of the page.
Console	This tab lets you receive error messages from internet explorer and send your own messages back from your code without changing the execution flow of your code. Console reminds me of the output window and the debug object in the Visual Studio. I wrote a blog talking about how to use the Console object to display messages.
Script	This tab allows you to quickly debug JScript complete with breakpoints and variable watches.
Profiler	This tab has a script profiler that allows you to analyze the performance of JavaScript code and can be used to check the performance of your scripts.
Network	This tab is for determining the traffic being sent across the network. It shows you all the traffic related to a page. You can see the time it takes for each item on a webpage to load and render.

Trying to cover every tab in detail is too much for one blog, but let me help you get started by introducing today’s My 5:

My 5 favourite features in the Internet Explorer F12 Developer Tools

(that’s what they call ‘em so now you know what keywords to use when you bing it, yes I said bing, didn’t you see the article?)

1. Find | Select element by click (CTRL+B)

How many times have you had to go digging through your HTML trying to find that one line of text with the missing accent, or a particular image. When you use Select element by click, you can just click on the element in the web browser and the matching HTML will be shown in the HTML pane below! (and there was much rejoicing)

2. Tools | Change User Agent String

You have a user complaining the site doesn’t work, but it works just fine for you, you ask them what browser they are using, it turns out its a different browser from the one you have installed on your machine. Change the User Agent string to one of the preselected browsers, or even specify a custom setting and voila! Now you can experience the web page the as if you were on a different browser. If you just want to check how the website works on different versions of Internet Explorer you can also use the menu option Browser Mode, browser mode will even let you simulate what happens when a user on IE9 visits a page in compatibility mode (I wrote a blog on compatibility mode a while ago, that’s the feature that you can use if you want the great features of IE9 but have to work with websites that seem messed up in IE9).

3. Tools | Outline Elements

Maybe I just like this one because I have a tendency towards making absolutely hideous web pages (I do not have a good eye for what colors look nice and so on), Outline elements helps you identify different parts of the web page. For example you could outline all the <div> tags in yellow, or all the <a> tags in blue so you can quickly find them on the page.

4. The Script Tab – formatting JavaScript

Often JavaScript is minimized on web pages which makes it hard to read. When you go the script tab, you can click on the Tools button and choose Format JavaScript from the drop down button.

This will turn your JavaScript from this jumbled mess

 function EmuController(a,b){this.impression=b;this.containerId=a;DataStore.set($(a),'emuController',this);return this;}copy_properties(EmuController,{fromContainer:function(a){var b=ge(a);if(!b)return null;return DataStore.get(b,'emuController');},getEventClass:function(a){return "emuEvent"+String(a).trim();}});copy_properties(EmuController.prototype,{EVENT_HANDLER_PATH:'/ajax/emu/end.php',CLICK:1,FAN:"fad_fan",event:function(c,b,d,a){var e={eid:this.impression,f:0,ui:this.containerId,en:c,a:1};if(b)e.ed=JSON.stringify(b);if(!a)var a=bagofholding;var f=new AsyncRequest().setURI(this.EVENT_HANDLER_PATH).setData(e).setErrorHandler(a);if(d)f.setHandler(d);f.send();},redirect:function(){var a={eid:this.impression,f:0,ui:this.containerId,en:this.CLICK,a:0,sig:Math.floor(Math.random()*65535)+65536};var b=new URI(this.EVENT_HANDLER_PATH);b.setQueryData(a);goURI(b);}});
var ShortClickHandlers={EVENT_NAME_CAME_BACK:'cameback',onclicked:function(a){if(this.onsite)return;if(a.button!==0||a.getModifiers().any)return;this.click_ts=(+new Date());if(this.listeners!==undefined)for(var b in this.listeners)this.listeners[b].remove();this.listeners={focus:Event.listen(window,'focus',ShortClickHandlers.oncameback.bind(this))};},oncameback:function(c){var b=(+new Date())-this.click_ts;this.listeners[c.type].remove();var a={click_ts:this.click_ts,length:b,trigger:c.type};this.sendData(ShortClickHandlers.EVENT_NAME_CAME_BACK,a);}};
function EmuTracker(a,c){this.base=EmuController.fromContainer(a);!this.base;this.onsite=c;var b=DOM.scry($(a),"a."+EmuController.getEventClass(EmuTracker.EVENT_CLICK));b.each(function(d){Event.listen(d,'click',ShortClickHandlers.onclicked.bind(this));}.bind(this));return this;}copy_properties(EmuTracker,{EVENT_CLICK:1});copy_properties(EmuTracker.prototype,{sendData:function(b,a){this.base.event(b,a);}});
(function(){if(!window.channel){window.channel={};}else if(channel.OK)return;var a='presence/';copy_properties(channel,{ON_CONNECT:a+'connect',ON_IDLE:a+'idle',ON_SHUTDOWN:a+'shutdown',ON_INVALID_HISTORY:a+'invalid_history',ON_CONFIG:a+'config',ON_ENTER_STATE:a+'enter_state',ON_EXIT_STATE:a+'exit_state',OK:'ok',ERROR:'error',ERROR_CONN:'error_conn',ERROR_MAX:'error_max',ERROR_MISSING:'error_missing',ERROR_MSG_TYPE:'error_msg_type',ERROR_REFRESH:'error_refresh',ERROR_SHUTDOWN:'error_shutdown',ERROR_DOS:'error_dos',HINT_AUTH:'shutdown auth',HINT_CONN:'shutdown conn',HINT_MAINT:'shutdown maint',reason_Unknown:0,reason_AsyncError:1,reason_TooLong:2,reason_Refresh:3,reason_RefreshDelay:4,reason_UIRestart:5,reason_NeedSeq:6,reason_PrevFailed:7,reason_IFrameLoadGiveUp:8,reason_IFrameLoadRetry:9,reason_IFrameLoadRetryWorked:10,reason_PageTransitionRetry:11,reason_IFrameLoadMaxSubdomain:12,reason_NoChannelInfo:13,reason_NoChannelHost:14,reason_ChannelUnknown:100,reason_ChannelNoCUser:101,reason_ChannelInvalidCUser:102,reason_ChannelInvalidChanstr:103,reason_ChannelChDistribTimeout:104,reason_ChannelGetChannelOther:105,reason_ChannelNodeShutdown:106,reason_ChannelTermination:107,reason_ChannelUserMismatch:108,reason_ChannelUserMismatchShady:109,reason_ChannelBadXs:110,reason_ChannelSeqNeg:111,reason_ChannelSeqTooBig:112,reason_ChannelSeqTooSmall:113,reason_ChannelUnexpectedJoin:114,reason_ChannelInvalidXsCookie:115,reason_ChannelRelocate:116,reason_ChannelWrongPartition:117,getArbiterType:function(b){return a+'message:'+b;}});})();
(function(){if(window.channel_cookie)return;window.channel_cookie={subdomainIndex:null,init:function(){var a=presenceCookieManager.getSubCookie('ch');this.retryInterval=presenceCookieManager.getSubCookie('ri')||0;if(!channel.getConfig('nosubdomain')){this.subdomainIndex=0;if(a&&a.sub){for(var b=0;b<a.sub.length;b++)if(!a.sub[b]){this.subdomainIndex=b;break;}if(b==a.sub.length)if(b==channel_manager.MAX_SUBDOMAINS&&URI().isSecure()){this.subdomainIndex=null;presence.error('channel: iframe max subdomains reached');channel_manager._sendIframeError(ChannelRebuildReasons.IFrameLoadMaxSubdomain);}else this.subdomainIndex=a.sub.length;}}presenceCookieManager.register('ch',this.getInfo.bind(this));var c=(function(){this._clearSubdomain=true;presence.doSync(true);}).bind(this);if(typeof window.onpageshow!='undefined'){Event.listen(window,'pagehide',c);}else onunloadRegister(c);},getInfo:function(){var b={};var c=channel.getConfig('host');var e=channel.getConfig('port');if(c){if(null!==this.subdomainIndex){var a=presenceCookieManager.getSubCookie('ch');var f=(a&&a.sub)?a.sub:[];var d=f.length;f[this.subdomainIndex]=this._clearSubdomain?0:1;b.sub=f.map(function(g){return g?1:0;});}b[channel.getConfig('user_channel')]=channel.getConfig('seq',0);}b.ri=this.retryInterval;return b;}};})();
(function(){if(!window.channel){window.channel={};}else if(channel.init)return;copy_properties(channel,{inner:function(){return this.manager.transport._iframe.contentWindow.transport;},_sitevars:{},_config:{userActive:new Date().getTime(),sessionID:(Math.random()*2147483648|0).toString(16)},init:function(){channel_cookie.init();this._config.subdomainIndex=channel_cookie.subdomainIndex;this.log=bind(this,'_log','log');this.error=bind(this,'_log','error');this.warn=bind(this,'_log','warn');if(typeof(UserActivity)!='undefined')UserActivity.subscribe(function(){this._config.userActive=new Date().getTime();}.bind(this));},_log:function(b,c){var d=this.manager&&this.manager.transport;var a='channel2:'+(d?(d.logName+':'):'');if(b=='log'){return false;}else if(b=='warn'){return presence.warn(a+c);}else if(b=='error')return presence.error(a+c);},log:function(a){this._log('log',a);},warn:function(a){this._log('warn',a);},error:function(a){this._log('error',a);},configure:function(){$A(arguments).each(copy_properties.bind(null,this._config));Arbiter.inform(channel.ON_CONFIG,this);},getConfig:function(b,a){return b in this._config?this._config[b]:a;}});})();
function SimpleDrag(a){Event.listen(a,'mousedown',this._start.bind(this));}Class.mixin(SimpleDrag,'Arbiter',{_start:function(event){this.inform('start',event);var b=ua.ie()<9?document.documentElement:window;var a=Event.listen(b,{selectstart:Event.prevent,mousemove:this.inform.bind(this,'update'),mouseup:function(event){for(var c in a)a[c].remove();this.inform('end',event);}.bind(this)});return false;}});
function ScrollableArea(){}copy_properties(ScrollableArea,{getInstance:function(a){var b=Parent.byClass(a,'uiScrollableArea');return b?DataStore.get(b,'ScrollableArea'):null;}});ScrollableArea.prototype={init:function(a,b){b=b||{};this._elem=a;this._wrap=DOM.find(a,'div.uiScrollableAreaWrap');this._body=DOM.find(this._wrap,'div.uiScrollableAreaBody');this._track=DOM.find(a,'div.uiScrollableAreaTrack');this._gripper=DOM.find(this._track,'div.uiScrollableAreaGripper');this._options=b;this.adjustGripper();this._listeners=[Event.listen(this._wrap,'scroll',this._handleScroll.bind(this))];if(b.fade!==false)this._listeners.push(Event.listen(a,'mouseenter',this.adjustGripper.shield(this)),Event.listen(a,'mouseenter',this.showScrollbar.shield(this)),Event.listen(a,'mousemove',this._handleMousemove.bind(this)),Event.listen(a,'mouseout',this.hideScrollbar.shield(this)));this.initDrag();DataStore.set(this._elem,'ScrollableArea',this);if(!b.persistent)onleaveRegister(this.destroy.bind(this));},initDrag:function(){var a=new SimpleDrag(this._gripper);a.subscribe('start',function(b,event){if(!((event.which&&event.which===1)||(event.button&&event.button===1)))return;var d=this._getPageY(event);var e=this._gripper.offsetTop;var f=a.subscribe('update',function(g,event){var j=this._getPageY(event)-d;var i=this._elem.clientHeight;var h=this._body.offsetHeight;var p=this._track.offsetHeight;var k=i/h*p;var m=h-this._wrap.offsetHeight;var l=e+j;var n=p-k;l=Math.max(Math.min(l,n),0);var o=l/n*m;this._wrap.scrollTop=o;}.bind(this));var c=a.subscribe('end',function(){a.unsubscribe(f);a.unsubscribe(c);});}.bind(this));},adjustGripper:function(){var b=this._elem.clientHeight;var a=this._body.offsetHeight;var e=this._track.offsetHeight;var c=b/a*e;if(c<e){CSS.setStyle(this._gripper,'height',c+'px');var d=this._wrap.scrollTop/a*e;CSS.setStyle(this._gripper,'top',d+'px');CSS.show(this._gripper);}else CSS.hide(this._gripper);this._checkContentBoundaries();return this;},_checkContentBoundaries:function(){var a=this._wrap.scrollTop;var b=this._wrap.scrollHeight-this._wrap.clientHeight;CSS.conditionClass(this._elem,'contentBefore',a>0);CSS.conditionClass(this._elem,'contentAfter',a<b);},destroy:function(){this._listeners.forEach(function(a){a.remove();});this._listeners.length=0;},_getPageX:function(event){return event.pageX!=null?event.pageX:event.clientX+document.body.scrollLeft;},_getPageY:function(event){return event.pageY!=null?event.pageY:event.clientY+document.body.scrollTop;},_handleMousemove:function(event){var a=Vector2.getElementPosition(this._track).x;var b=Vector2.getElementDimensions(this._track).x;if(Math.abs(a+b/2-this._getPageX(event))<25){this.showScrollbar(false);}else this.hideScrollbar();},_handleScroll:function(event){this.adjustGripper();if(this._options.fade!==false)this.showScrollbar();},hideScrollbar:function(){if(!this._scrollbarVisible)return this;this._scrollbarVisible=false;if(this._hideTimeout){clearTimeout(this._hideTimeout);this._hideTimeout=null;}this._hideTimeout=function(){if(this._scrollbarAnimation){this._scrollbarAnimation.stop();this._scrollbarAnimation=null;}this._scrollbarAnimation=animation(this._track).from('opacity',1).to('opacity',0).duration(250).ondone(CSS.addClass.curry(this._track,'invisible_elem')).go();}.bind(this).defer(750);return this;},showScrollbar:function(a){if(this._scrollbarVisible)return this;this._scrollbarVisible=true;if(this._hideTimeout){clearTimeout(this._hideTimeout);this._hideTimeout=null;}if(this._scrollbarAnimation){this._scrollbarAnimation.stop();this._scrollbarAnimation=null;}CSS.setStyle(this._track,'opacity',1);CSS.removeClass(this._track,'invisible_elem');if(a!==false)this.hideScrollbar();return this;},scrollToBottom:function(){animation(this._wrap).to('scrollTop',this._wrap.scrollHeight).ease(animation.ease.end).go();}};
FriendRequestMessage={STATUS:'FriendRequest/change',UNFRIEND:

To this nicely formatted and readable code

 function EmuController(a,b){
    this.impression=b;
    this.containerId=a;
    DataStore.set($(a),'emuController',this);
    return this;
}
copy_properties(EmuController,{
    fromContainer:function(a){
        var b=ge(a);
        if(!b)return null;
        return DataStore.get(b,'emuController');
    }
    ,getEventClass:function(a){

5. The Network Tab for Audio and Video

Video and Audio can be a real challenge to work with, and when a video doesn’t play I am never sure if the problem is with my code, the MIME type settings, browser compatibility, or the video itself! By using the network tab to capture my page load I was able to determine whether the problem when my HTML5 video or audio element didn’t work was due to MIME type issues by checking the value in the Type column for that element on the page. You can use the network tab for lots of other great profiling as well, but I have found the type column a nice easy way to check my MIME types.

If you haven’t had a chance yet download the latest version of Internet Explorer today and start trying out the F12 Developer Tools!