Is there a browser that will allow me to trace the execution of Javascript events? For example, for some random site online, if I click on something in one area of the page, it causes the text in some other area of the page to get updated with some new text. I would like to be able to trace what happens from the click all the way to the value being updated. When I say trace I mean that I would like the browser to tell me the name of the Javascript function that handles the click (and which file it is located in) and which Javascript function updates the value on the page.
The solution must work for any random website on the internet.
In chrome you can trace js codes in website with DEBUG mode.
Open Chrome.
Open a website.
Open Dev Tool with press F12.
On the menu click Sources. Now you can see all js files at there. And there is a debug panel. You can start, renew, break, trace a code line with these tools.
On js code panel you can put breakpoints on the line numbers.
Press F5 and refresh the page. Code will pause and you can trace js values.
Related
Is there anyway to prevent changes to web pages such as a live chat or a video feed? Im guessing its a javascript that times out the webpage and then exits it or prevents further entry.
I saw this question: Freeze screen in chrome debugger / DevTools panel for popover inspection?
What I did was I inspected the element, then went to the line of code and then clicked on :hover but the script still executed and locked me out. Any other ways you can think of to prevent changes being made to a page?
Chrome allows you to disable JavaScript on certain pages, to do so click on the globe of the URL bar and it will show some permission options for the site you are. There disable JavaScript.
How to deliberately freeze javascript in chrome (plugin/console)
Found another solution in the link above:
Open Chrome javascript console
Go to "sources"
On the right side, click the little "pause" icon, or press F8 to pause script execution.
Greeting
I'm trying to debug java-script with qt web-kit but its not working.
This is what i do. I right click on qt web-view and choose "Inspect", In inspector window, I go to "Scripts" tab, I choose "Only enable for this session / Always enable" then press "Enable Debugging" button. In java-script file, I place break point in function (by clicking on line number). I can see the line in "Breakpoints" group in right side of window as well. I perform a specific action which causes function's launch (in UI), But nothing happens, The break point not hit and function returns. I invoke function manually from the console by typing its name and arguments and still nothing happens. Function return without hitting break point.
I Also enabled JavascriptEnabled.
Im using QT 4.8 and Visual Studio 2008.
Can any want tell me whats wrong here ?!
Thanks in advanced
As I F10 or F11 through my javascript code in Chrome Dev Tools, sometime the execution will move to a line that is not currently in the view (same file though).
How do I tell Chrome to bring that line of code into the view?
As you step through the code you should be able to open the call stack panel to the right of the sources window and double click on the breakpoint you wish to jump to.
I've a HTML page which contains some hacked script which contains something like, e.g.
setTimeout(function () {
window.location = window.location;
}, 3000);
But assume this page used a lot of minified JS and span over multiple files, with Chrome/Firefox developer tool, how to spot the above section of code from multiple files? i.e. stop the execution and break on the currently running line?
"spot(ting) the above section of code" and "stop(ping) the execution and break on the currently running line" are completely different things.
spot(ting) the above section of code
To find code anywhere in the various source files, your can use Chrome's Dev Tools' global search feature:
Open Dev Tools (F12, Ctrl+Shift+I, or via the menu)
Switch to the Sources pane
Press Ctrl+Shift+F (probably Cmd+Shift+F on a Mac)
Type what you want to find
stop(ping) the execution and break on the currently running line
Open Dev Tools (F12, Ctrl+Shift+I, or via the menu)
Switch to the Sources pane
Click the pause button (it looks like two vertical bars)
Dev Tools should break on the next bit of JavaScript that tries to run (according to this page on developer.chrome.com).
If the code is large and unknown to you, one option is to use the Profiler.
There's a "Profiles" tab in Chrome devtools and a "Performance" tab in Firefox devtools.
Each of these tools behave pretty much the same in that you start a recording, then wait (or perform any action on the page that you know leads to script running), then stop the recording.
The panel in the middle is going to display a call tree of all the scripts that ran during that period of time with columns that should, hopefully, tell you more about what took time.
Using that call tree, you can then drill down to discover what got executed exactly and then from there, jump to the actual line in the script.
Here's the chrome devtools profiler documentation page and here's the firefox devtools counterpart.
One other option you have, using the firefox devtools is the tracer. A tracer is a tool that record everything that occurred at the javascript level: what functions got called, what arguments where passed, what value got returned, what functions did those, in turn, called, ...
To check it out:
open about:config in firefox, then switch pref "devtools.debugger.tracer" to true.
Then open the devtools and switch to the debugger panel.
Then click on the double arrow icon, next to the pause/step over/step in/ step out buttons.
This will start the tracing and switch the side bar to the "traces" panel.
Click again to end the recording.
You should see the trace of what got executed. If you click on any entry in the trace, you'll see the associated script and in the sidebar, the arguments and return values.
I'm currently moving a website from self hosted onto a CMS system. The current site uses a modal popup script called SqueezeBox.js
I've copied the code across exactly how it looks on the current website, however the modal popup box isn't triggering when I click on a thumbnail image.
Looking at the code in the header I've spotted that the CMS I'm using is also calling a number of other javascript files and I'm wondering if one of them is causing a conflict.
What's the best way to find out if this is the case? I've tried Firefox's plugin Web Developer but can't see anything in the Error Console. However I'm not 100% sure I'm using it correctly. Can anyone else point me in the direction of a simple to use javascript conflict detector?
Cheers
Adam
If you have Google Chrome, open up the Developer Tools and you can go into the 'scripts' tab, open up your javascript files and look for the click handler.. click along the side of the code to set a breakpoint, then when the code reaches that spot (if you click it, for example), it will pause, and then in the Developer Tools you can see what functions are being called where as you step through the code. You can also hover over any variable in the code window to see its value. Very handy! You can then see if it's getting into your plugin at all (you can do this as well by setting a breakpoint inside the plugin at a place like the first line that will always be accessed when its run).
I believe you can do the same thing with Firebug
It's a bit of a different thinking process to get into (step into, step over, turning breakpoints on and off etc) but it's extremely useful.
A more simple way of checking where problems are occuring is by adding an alert('im working); or something similar to code you're not sure if it's working. You can also alert a variable to see what the value is at that point. You can also use console command to print it to firebug's console. These are doing things that breakpoints/debugging do for you except with the debugging you don't need to change your code.
If there is a javascript error, then the easies way is using firebug or the Chrome Inspector (right click on the thumbnail and choose "Inspect element"). Open the console tab of either and refresh the page. If there is an error, it will be reported in the console and provide a link to the relevant line.
If there is no error being reported, then the code's logic is preventing the box from being displayed. You'll need to step through the code to find the error. Look at what function is being called from the click handler of the thumbnail image. Go to that function in either tool and place a breakpoint on the first line of the function. Click the thumbnail again and the code will pause on that line. From there you can step through the code and see which code branch is followed. There's likely a sanity check at some point that fails and causes the code to bomb out.