When I'm in a complex website such as Facebook and write a comment and push Enter there is an event fired that starts everything. Can I somehow observe which events are fired and when (and eventually somehow trace/step them)?
So in general, I'm looking for a tool capable debugging a website in this way. Is there any way?
If you are using devtools of Google Chrome, there is an Event Listeners tab that could help. See the attached picture.
There, I have selected the "Post your answer" button of this very question and as you can see, the EventListeners tab shows that there is at least an onSubmit event listener attached.
One of the debugging tool that i am using and works well for me is firebug in mozila.
you can read about firebug Here
With fire bug you can notice everything like webpage is making how much ajax call, which script is binned with which element. even you can also easily debug the css and design elements. firebug will help you more to debug the website on browser.
Related
When I try to click on the "Inspect this" field on a popup which appears only onMouseHover event it can become very annoying.
https://youtu.be/4lPcO00MUYk
And since it's frequent to attach a javascript behavior to any DOM element event through selectors I can't imagine how to debug this web pages.
Any suggestion?
I've found a question which may help with my problem, but also #Kaddath solution is very interesting.
See: https://stackoverflow.com/a/15923770/196210
Using Chrome , I need to debug the java-script handler that is executed when a specific button is clicked, without searching the java-script files.
Can I use Chrome's "inspect element" for the button to find java-script handler?
Or, is there a recommended tool?
How to achieve this?
p.s: Think of a complex app within a website, I need to debug the logic behind some buttons..
When you open the developer tools on the element tab if you select the element to debug you will see at your right a tab Event Listener. It is with the Styles tab. there you can inspect the event listener. In my opinion the best way is to add break points on the sources. You'll see.
This question already has answers here:
Using Chrome, how to find to which events are bound to an element
(8 answers)
Closed 8 years ago.
I am looking at the Bing Maps site. I am opening up the my places editor and clicking the polyline tool in the drawing toolbar.
I would like to discover what javascript runs when I click on tools in the drawing toolbar.
I have looked at the html and there is no onclick event declared on the element.
I have done text searches on all of the scripts referenced by the page, for the ID of the polyline tool element. This was to try to find javascript that attaches a click event to the element, but I got no matches at all.
There must be some script running when I click on a tool. How do I find out what script is executing when I click the tool divs in the toolbar?
I don't think there is anyway I can set breakpoints if I don't first know what script to set them on. Is there anyway I can trap the javascript that runs to discover what it is, either in IE F12 developer tools or in firebug?
You can have a look at the "Event Listeners" panel in Chrome, it has detailed information about each listener attached to an element.
In Chrome Developer Tools click on the timeline tab, uncheck "Loading" and "Rendering", then click the record button (filled circle). Trigger your event by clicking on the button and then stop recording by clicking the circle again. Find your event in the timeline and expand it by clicking on the arrow beside it. On the left it will tell you which function the event called.
I've used the Profiler in Chrome's debug tools for this purpose before.
Open the site in Chrome, F12 to get the debug tool open. In the tabs at the top of the tool, click Profiles.
Make sure Collect JavaScript CPU Profile is selected, and hit Start, then click on the polyline tool you're curious about, and hit Stop. The profiler should now list out all Javascript calls made while the profiler was active.
Firebug probably has something similar.
To locate a potential event handler for a particular element that has been added dynamically try performing a search in all sources of classnames and ids. Once you've found an event handler you can set a breakpoint and verify.
Google Chrome has a global search that works great.
Open up your debugger and start the profiler. Click on what ever you want. Look at what the profiler and see what was called.
I am trying to reverse engineer a Microsoft CRM 2011 web page. The page loads a massive number of scripts and HTML. My current development focus is on the click event of a checkbox element on the page. Clicking the element causes behavior on the page to change, and I want to walk through the code that handles this.
The problem is the checkbox's click handler is attached during page load via an anonymous method. So the code is there, but trying to find it is asking one to locate a needle in a haystack.
Is there a technique using the Internet Explorer debugging tools to somehow make the debugger stop when the checkbox is clicked? There may not be, but I thought I would ask.
Your best bet is to run this in the console:
document.getElementById('theCheckBoxId').onclick
If null appears in the console, you can continue reading. Otherwise the onclick handler and it's code should appear right there in the console.
Use Chrome's dev tools: Right click something on the page -> inspect element. You'll see this:
Go to "SOURCES" (no longer called "Scripts") and there is a '||' Pause button as you see in the screenshot. If the page doesn't fail, you can check the checkbox, and since scripts are paused, you'll see the code for the anonymous function become highlighted and the page will be frozen. You can then use the tools to step through the code.
However, we can certainly better help you with what you actually want from the page...
You can also use attach a onbeforescriptexecute from the console: https://developer.mozilla.org/en/DOM/element.onbeforescriptexecute
You would be something like this in the console:
document.getElementById('theCheckBoxId').onbeforescriptexecute = function (e) {
alert('hey same thing as pausing the script!');
console.error('script with this id about to run: ' + e.target.id);
//Could also try .src .innerText etc.
//Reference this: https://developer.mozilla.org/en/DOM/element.onbeforescriptexecute
//the full argument to checkout in the console:
console.error(e);
};
You can also play around with the currentScript method: https://developer.mozilla.org/en/DOM/document.currentScript
You can also right click and inspect the check box, and then on the right panel of dev tools, look at the 'Click' event listener code, but often this is garbled and hard to work with.
It sounds like you have no way of modifying the anonymous function that is tied to the checkbox click event. If not, perhaps you can create a second event handler, but define it before the definition of the existing event handler.
Event handlers in the browser typically fire in the order they were defined. See http://jsfiddle.net/aroder/kkYfX/2/. If you defined your own event handler, it will give you a place to attach the debugger at least somewhere close to the anonymous function you are trying to step through.
Also, use the debugger statement to automatically break your code. If you are using IE, ensure the options under Tools > Options > Advanced > Disable Script Debugging (Internet Explorer) is UNchecked.
<script>
// the debugger statement will automatically break in IE dev tools, Firebug, and Chrome dev tools
debugger;
</script>
Older version of IE is pretty lame specially when it comes to debugging AJAX applications. Firebug is the best that I have seen. It lets you replace an existing javascript function with your own. This is what I suggest.
Open the web application in Firefox
Copy sourcecode of existing function
Format it and add the following statement to the function at the place where you want it to stop and inspect the variables.
debugger;
Paste the new code in Firebug's console window and click on Run .. that's it!
I have a set of pages that have tons of JavaScript on it: Table sorting, AJAX calls, autocomplete, dynamically hiding and displaying areas of the page, etc... The problem that I am seeing is when the data on said page gets large a delay (browser freezes) is noticed when leaving the page. This delay happens when the user clicks away, closes the browser, or executes a form submit. I want to see if the problem is caused by JavaScript. What tool could I use to find out? Firebug doesn't seem to work in this scenario.
The only place unload is mentioned in the codebase is in jquery.js and ui.tabs.js (jquery ui)
Are there any onunload event handlers attached (to body, window, form etc.)? If so, it would be a good starting point to investigate.
[Edit]: Apparently jQuery runs a loop unbinding all the events attached to every element. This is to prevent memory leaks in IE (created due to event handler closures referencing the element they are listening to). This could create a delay if your DOM is very complex.
Can you try commenting this portion out in jQuery code and see if that is causing the problem?
[Edit 2]: The window unload seems to have been improved in newer versions of jQuery (1.3+). What version are you using?
Inline Code Finder is a firefox addin (well, really it's a firebug addin) that shows you visually what events are attached where and when they're invoked.