I'm working on a big application. In my application a lightbox opens up on page load and refresh. There are many JavaScript files included in the application, and many developers have worked on it. I'm trying to debug and identify the JS code that is causing that lightbox to open up so that I could edit it.
I tried adding breakpoint in Chrome developer's tool on Load (see image below), but when it stops on first breakpoint, the lightbox is already on the screen. Which means the code for lightbox was rendered before first load event listener fired up.
Is there any way I can find out from where that lightbox code is opening up?
P.S: I'm also unsure what is the exact code syntax used to open up the lightbox, otherwise I would have searched the source files for that syntax.
UPDATE: On further inspection, I've found out when these lines in the jQuery library file are executed, the lightbox shows up.
These lines appear to be event loop triggering. I'm not sure if this information is any useful for solving this problem.
You can use
console.trace();
To see what functions where invoced to get to the line in code you put the .trace in.
Since you found a function inside the jQuery library that is somehow involved in the opening you should put it there.
Aditiinally you can put a code-sided breakpoint underneath it by calling
debugger;
If not already. consider using a local, uncompressed version of jq for easier debugging.
I'm using CasperJS to scrape a website. The page source has a <noscript> tag, and therefore is not showing the page I need to scrape, because it claims I don't have JavaScript enabled.
javascriptEnabled is true by default in CasperJS, but I added it to my initialization anyway, to no avail.
Any work arounds to fix this issue? It might also be an issue with PhantomJS...
Ok this issue has been fixed -- I did the following, if anyone has any questions. The HTML was rendered by the JavaScript, which took a long time to load, so open it like you would normally in a browser, and find an element that only appears when the javascript loads -- note doing view source doesn't work you have to inspect element (you get current DOM).
I then did:
casper.waitForSelector('.SOME_CLASS', function() {
this.echo(this.getHTML('.SOME_CLASS'));
this.echo(this.getElementInfo('.SOME_CLASS').text);
});
This allows the page to stop and load the javascript.
I am working on a project which involves ad-detection. I wanted to leverage ad block plus code. But I am struggling with understanding it.
I am using adblock plus for chrome and using chrome debugger to step through the code, but whatever breakpoints i set inside most of the javascript files, the control is not getting there. I am only able to see the control going to include.preload.js. I have added the source folder to work space.
Also content script is showing only a few files and breakpoint set in inlcude.preload.js in content scripts is working, but breakpoints set anywhere else dont seem to get hit, not even if they are set in source tree.
Any pointers will be very helpful. I am struggling as I am new to this domain. If there are any books/resources to help understand the working of ad block plus better, please suggest. Thanks in advance.
include.preload.js and include.postload.js only contain the code that's being injected into the page. The core code of the extension is running in its background page which you can debug like this:
Go to chrome://extensions
Check the "Developer mode" checkbox in the top-right corner
Click on the "Background page" link underneath the Adblock Plus entry
When I right click on the icon for my extension-in-development and click Inspect Popup (or when I click the icon and choose "Inspect Element") and look under the "Sources" tab, my .js file is nowhere to be seen - only a long list of inspect-able files like apitest, devtools, json_schema, etc. I can, however, find the code through the Elements tab by following the link in the .html file, but that doesn't bring to anywhere where I can actual debugging.
I've also loaded the "Hello, world" extension that Google's tutorial provides, and when I Inspect that one, its .js file is right there. I can't imagine what I've done differently from the tutorial example to cause this.
It's Chrome version 22.0.1229.94 run in a Linux VM. If there's any more information I should be providing, please let me know.
Type location.reload(true) in the console.
http://developer.chrome.com/extensions/tut_debugging.html
If I understand your question right,
Under the sources tab, there are two more tabs, one says Sources and the other says Content scripts. You need to click on the content scripts tab, and there you will find what you are looking for.
Okay So I figured it out, simply click on you extension icon, and a little dialog will pop up, then right click on it and click on inspect element. You can figure it out from there I reckon. (My other answer would be good if it was a content script, but this is a popup script.)
How do I "dynamically" edit JavaScript code in the Chrome debugger? It's not for me, so I don't have access to the source file. I want to edit code and see what effects they have on the page, in this case stopping an animation from queuing up a bunch of times.
I came across this today, when I was playing around with someone else's website.
I realized I could attach a break-point in the debugger to some line of code before what I wanted to dynamically edit. And since break-points stay even after a reload of the page, I was able to edit the changes I wanted while paused at break-point and then continued to let the page load.
So as a quick work around, and if it works with your situation:
Add a break-point at an earlier point in the script
Reload page
Edit your changes into the code
CTRL + s (save changes)
Unpause the debugger
You can use the built-in JavaScript debugger in Chrome Developer Tools under the "Scripts" tab (in later versions it's the "Sources" tab), but changes you apply to the code are expressed only at the time when execution passes through them. That means changes to the code that is not running after the page loads will not have an effect. Unlike e.g. changes to the code residing in the mouseover handlers, which you can test on the fly.
There is a video from Google I/O 2010 event introducing other capabilities of Chrome Developer Tools.
You can use "Overrides" in Chrome to persist javascript changes between page loads, even where you aren't hosting the original source.
Create a folder under Developer Tools > Sources > Overrides
Chrome will ask for permission to the folder, click Allow
Edit the file in Sources>Page then save (ctrl-s). A purple dot will indicate the file is saved locally.
This is what you are looking for:
1.- Navigate to the Source tab and open the javascript file
2.- Edit the file, right-click it and a menu will appear: click Save and save it locally.
In order to view the diff or revert your changes, right-click and select the option Local Modifications... from the menu. You will see your changes diff with respect to the original file if you expand the timestamp shown.
More detailed info here: http://www.sitepoint.com/edit-source-files-in-chrome/
Chrome Overrides
Open the JS file in the sources panel.
Right Click on script src URL > Reveal in Sources panel
Make sure "Enable Local Overrides" is checked.
Right Click anywhere in the JS file > Save for overrides
All Set!
Just edit the file, and save with CMD/CTRL + S. Now whenever you refresh the page, it'll use the modified file. (As long as the filename remains the same)
You'll know it's working if you see a purple dot in the file icon.
Place a breakpoint
Right click on the breakpoint and select 'Edit breakpoint'
Insert your code. Use SHIFT+ENTER to create a new line.
Pretty easy, go to the 'scripts' tab. And select the source file you want and double-click any line to edit it.
If its javascript that runs on a button click, then making the change under Sources>Sources (in the developer tools in chrome ) and pressing Ctrl +S to save, is enough. I do this all the time.
If you refresh the page, your javascript changes would be gone, but chrome will still remember your break points.
As this is quite popular question that deals with live-editing of JS, I want to point out another useful option. As described by svjacob in his answer:
I realized I could attach a break-point in the debugger to some line of code before what I wanted to dynamically edit. And since break-points stay even after a reload of the page, I was able to edit the changes I wanted while paused at break-point and then continued to let the page load.
The above solution didn't work for me for quite large JS (webpack bundle - 3.21MB minified version, 130k lines of code in prettified version) - chrome crashed and asked for page reloading which reverted any saved changes. The way to go in this case was Fiddler where you can set AutoRespond option to replace any remote resource with any local file from your computer - see this SO question for details.
In my case I also had to add CORS headers to fiddler to successfully mock response.
Now google chrome has introduce new feature. By Using this feature You can edit you code in chrome browse. (Permanent change on code location)
For that Press F12 --> Source Tab -- (right side) --> File System - in that please select your location of code. and then chrome browser will ask you permission and after that code will be sink with green color. and you can modify your code and it will also reflect on you code location (It means it will Permanent change)
Thanks
Just like #mark 's answer, we can create a Snippets in Chrome DevTools, to override the default JavaScript. Finally, we can see what effects they have on the page.
here's a gentle introduction to the js debugger in chrome that i wrote. Maybe it will help others looking for info on this: http://meeech.amihod.com/getting-started-with-javascript-debugging-in-chrome/
you can edit the javascrpit files dynamically in the Chrome debugger, under the Sources tab, however your changes will be lost if you refresh the page, to pause page loading before doing your changes, you will need to set a break point then reload the page and edit your changes and finally unpause the debugger to see your changes take effect.
I was looking for a way to change the script and debug that new script. Way I managed to do that is:
Set the breakpoint in the first line of the script you want to change and debug.
Reload the page so the breakpoint is being hit
Paste your new script and set desired breakpoints in it
Ctrl+s, and the page will refresh causing that breakpoint in first line to be hit.
F8 to continue, and now your newly pasted script replaces original one as long as no redirections and reloads are made.
Chrome DevTools has a Snippets panel where you can create and edit JavaScript code as you would in an editor, and execute it.
Open DevTools, then select the Sources panel, then select the Snippets tab.
https://developers.google.com/web/tools/chrome-devtools/snippets