I am trying to understand how to get from the chrome debugger the following info : there is an event on page triggered by a click on an input file type tag. But it is impossible for me to trace back the mecanism : which js file is called when the event is triggered. Is there a way do get this info from the debugger ?
Do you have a look at the Event Listeners entry in the right-hand window? If I right-click the 'Google-Chrome' tag at the bottom of your post, and select Inspect Element, I get the html tag highlighted. If I then look in the right-hand pane at the Event Listeners, I can see that this element has handlers for blur, click, keyup, keydown, mousedown, mouseout, mouseover. Yet just looking at the html I can't see that. If I expand the event handlers, I can see that they all point to "jquery.min.js : 3". This is because the file has been minimized and is only 4 lines - each of which is probably 20 or 25,000 chars long. Minimized scripts are difficult to analyse unfortunately.
Try it with a page that doesn't use minimizes scripts and you can click the link in the event handler window to be taken directly to the pertinant function - unfortunately, you are taken to the start of the line concerned, which makes jquery.min.js a waste of time to do this with. You can always use the non-minified version of a script for debugging purposes, switching over to the minified version for production.
With other's pages, you can sometimes get away with saving a local copy, before linking an unminified version of the script.
Related
I get this error in the Chrome console every time I try to evaluate an expression.
EvalError: Possible side-effect in debug-evaluate
What could be causing it?
I think I found the issue, reading through a discussion on an electron issues board.
It could potentially be caused by this: [inspector] Add custom error dispatch machinery for debug evaluate.
And hopefully fixed in this: [inspector] Don't trigger window.onerror with side-effects disabled.
This was an oversight in https://crrev.com/c/3557234, which led to a really weird developer experience: once a window.onerror handler was installed, typing into the Console or other side-effect free debug evaluations triggered this handler.
The website you are inspecting contains an onerror event listener.
A new bug in the latest version of Chrome triggers this event every time an expression is evaluated in DevTools. This includes live expressions and the console.
If this is your own website, add this line of JavaScript to your event listener to ignore any errors triggered outside of a script, where script is the second argument of the event listener function:
if(!script.endsWith(".js")) return;
Note that this will only work for external JavaScript (in .js files), in the case of JavaScript embedded in HTML <script> tags, it will disable your event listener entirely.
If this is not your website, you can temporarily disable the event listener in DevTools, like this:
At the top of DevTools, open the "Elements" tab
Press "ยป", on the right of "Styles", "Computed", "Layout"
Choose "Event listeners"
Find and expand "onerror"
Click "Remove"
This will remove the event listener, but the issue will return after you refresh the page.
Hopefully the next version of Chrome will fix this bug.
With this code I want to create an event listener for whenever chrome storage updates.
I want 2 things to happen when the event listener is triggered:
The code will console log the updated values. This part works.
I want the HTML for the extension (the document that opens in the corner when you click the icon) to update and render the data value that is in chrome storage. This is that part I need help with.
chrome.storage.onChanged.addListener(function(changes, namespace) {
//part 1
console.log('New data type is %s. New value is %s',
changes['type'].newValue, changes['data'].newValue)
//part 2
document.getElementById('output').innerHTML =
changes['data'].newValue
});
I realize that calling "document" inside the function doesn't make sense, but I'm unsure how to move forward to get it to render in the extension's HTML.
I tried creating an event listener for when the context menu is accessed (users can update the chrome storage but clicking a button in the context menu) but I couldn't get it to work. Also the event should trigger when chrome storage is updated, not when the context menu is simply accessed.
Right now I get this error:
Error in event handler: TypeError: Cannot set property 'innerHTML' of null
(There is an element with id 'output', so that isn't the problem)
Thanks for your help!
The background script runs in a separate hidden background page. It's not related to the browserAction or pageAction popup page, it doesn't have any of the popup page elements, its DOM is empty except for the auto-generated script tags of the background scripts.
The popup is also a separate page and just like any normal page its environment/DOM exists only when the page is shown. You can't modify it when it's not shown. You can't show it from your code in general case either.
Solution 1
Put that onChanged listener in popup.js script that's loaded in your popup.html (declared as "browser_action": {"default_popup":"popup.html"} in your manifest.json) using the standard <script src="popup.js"></script> tag. It will update the popup page if it's shown, and to display the current values when the popup opens read them with chrome.storage.local.get or chrome.storage.sync.get depending on which storage you're using in your extension.
Solution 2
Use chrome.notifications API to show a small notification at the bottom of the screen, see also the official demo extensions.
Solution 3
Use chrome.browserAction.setBadgeText to display short text like a temperature right under the extension icon. Don't forget to declare at least "browser_action": {} in your manifest.json.
I'm following this tutorial on how to use DevTools to insert breakpoints. I've opened the example page and have added a breakpoint on the click event, as in part 2 of the tutorial.
However, when I click the button, DevTools does not highlight function onClick() { in the get-started.js file, as the tutorial says it will. Instead, it highlights a minified function in a minified file (end.min.js):
Why is this happening? And how can I fix it? I would like to follow the tutorial, but it's pretty difficult with the breakpoint being added to the minified file.
I am not sure where end.min.js is even coming from: the Network tab doesn't show it being loaded. I'm not sure if it's related, but when I try to view the source of the page, Chrome shows the "loading" icon forever.
Is Chrome doing something clever with
It seems like an extension (I'd say a password manager) is adding event listeners too, and your breakpoint first catches this listener.
You can either test with the extension disabled (you may need to refresh the page), or just press "Resume" to go to the next listener.
Are you sure you're following the tutorial? I have followed this:
DevTools lets you pause your code in the middle of its execution, and
examine the values of all variables at that moment in time. The tool
for pausing your code is called a breakpoint. Try it now:
Go back to the demo and open DevTools by pressing Command+Option+I (Mac) or Control+Shift+I (Windows, Linux).
Click the Sources tab.
Click Event Listener Breakpoints to expand the section. DevTools
reveals a list of expandable event categories, such as Animation and
Clipboard.
Next to the Mouse event category, click Expand
Check the
click checkbox.
And the expected error shows:
Also you have to activate pause on caught exceptions, and seeing the image that you have provided it seems like you don't have that activated.
But I see if you open DevTools when you reload the page, another error pops up, maybe if you close DevTools, reload the page and try again?
I have a weird situation. One of my users is using functionality of Chrome (current version, 49, 50), that he drags and drops a file from his folder on local computer to normal input type=file button in a form on the webpage. Once again, let me stress it even more, its normal html input, no fancy javascript, no drag&drop events and handlers, nothing like this. It just takes the name of the dragged file and puts it into the input field, as like he selected it via "normal" way, opening the file select window, locating file on harddrive, selecting the file and confirming.
In some specific situation, this stops working (while doing some edits in the page via javascript / ajax), and I need to "reenable" it.
But, and that is my question, I haven't found any documentation of this "feature" in Google Chrome (or maybe some other browsers as well, I don't know). Why it works, how it works, how it should work and what to do if it stops working :) Does anyone has any experience with this ? The only way how to "fix" it now is to reload the page. I'd love to solve it ... :)
EDIT 1 : I just did a quick test, it works and bugs the same way in Firefox on Win. It doesn't show any error in dev console or any message, it just doesn't add the file as expected.
I've found it. The previous discussion with deceze pointed me to test the javascripts I have on the page, that do not "interfere" with the input type=file ... they weren't any such scripts, but I've found that after doubleclick on the table (that I'm using for editing) this script is being called
$(document).bind('drop dragover', function (e) {
e.preventDefault();
});
and there wasn't any unbind action when table is saved ... this caused the drag and drop everywhere on the page to stop working after the edit.
I've been working on a new website and practicing my JS/jQuery/AJaxy skills. Last night I wanted to take a look at how long the page was taking to render and see if there were any areas I could clean up to increase speed. While the page loads in about 200 - 300 ms every time, I'm seeing a large amount of blank space between resource loads under the network inspector.
http://i.imgur.com/7ng6m.jpg
Has anyone else seen this or know what I can do to minimize that time (talking about the blank space between like the html and the first css file)?
Quite possibly it is caused by the extensions you have installed. AdBlock, LastPass and Google quick scroll took altogether about 200 ms on my machine.
Unfortunately, these extensions are invoked on every site and block loading the additional resources.
Try it with out of the box browser setup, the loading time will increase tremendously.
You've got a bunch of images loaded just after the page has been loaded (the load and DOMContentLoaded events have fired - the blue and red vertical lines across the Timeline). I can see that the images are loaded by the JQuery library (the Initiator column), perhaps to build a gallery or something.
So, the case is that JQuery loads the images after the page load, presumably in the onload handler (this can look like $(document).ready(handler) in your code, but other options are possible, too).
The delay between the initial page load and requesting the first resources is almost certainly caused by Chrome extensions. To find the culprit: Record a timeline in the Timeline tab in Chrome Developer Tools; Identify the scripts that are running during the Parse HTML phase; Work out which extensions they're from.
To record a timeline:
Open the timeline tab and click record.
Reload the page and then stop the recording. (A couple of seconds should be enough.)
To find the culprit:
Find the first main Parse HTML block on the timeline. On the row below you will probably see one or more Evaluate Script blocks. These are the culprits.
Click on one of the Evaluate Script blocks and find the script name in the bottom pane. Mouse-over the script name. The tooltip will have the URL of the script, which should be of the form chrome-extension://{long_identifier}/{path}
Memorise the first few letters of the identifier and search for it in the chrome://extensions/ page. This tells you which extension is causing the problem. Try disabling it - you should see a difference.
Repeat for the other Evaluate Script blocks.
In my case, I have 20 extensions installed but only two were causing a delay: LastPass and Fauxbar. I've chosen to leave them enabled because for me the productivity benefit of these extensions outweighs the downside of the added latency.