Develop Reference

In a web browser, how to find out what triggers a hidden CSS class to appear in javascript?

As a freelance Wordpress developer I find myself thrown into projects where things are just 'broken' - with the problems regularly ending up being some kind of path issue/syntax error/etc in javascript.
I am in the situation right now where I am trying to get something that works in Site A to work on Site B. Basically the problem involves a mouse over event that causes a div with class name 'overlay-ico' to appear.
I'm sure there must be some kind of debug tool in Chrome, Firefox, etc that allows me to easily do this without reviewing all the source code?
Update:
I am familiar with being able to inspect the HTML (at least in a basic way), but I don't see how this shows me what would trigger an event to occur.
I am also know that there is a console, which as I understand it, only outputs errors, or something that has been explicitly directed to console output.
There must be somewhere in the code that is waiting for a mouse over event, that triggers 'overlay-ico' to appear. I'm sure I could do it if I did a search for 'overlay-ico' through all the source code - but I'm thinking there must be a faster way to find it.

In Windows, F12 opens the debug panel in most browsers.
In Chrome, you can inspect an element and then click into the Event Listeners tab in the right pane. That may show what you're after. It's hard to say without seeing it.

HTML jquery onclick event not working on dynamically-created links on Android phones only

I am having an issue where dynamically-created links are working on all devices I have tested (in all desktop browsers, on my iPhone, on my iPad, and on my Samsung Galaxy Tablets Chrome Browser), but will not work when clicked on Android phones (I've tested on three Android phones running Chrome, sorry don't have the Chrome versions, but one phone is really new and the others are 1-2 years old at most).
I am dynamically-creating the links to add items to a cart (inside of a larger dynamically-created entity) in a loop.
The link in question is constructed basically like this:
var itemHTML = "";
...
itemHtml += '...<span>\n'
...
Where gAddLink is just a standard URL. I am then inserting that itemHTML (in addition to other HTML) onto the page dynamically using document.write().
Since this is being dynamically created on page load (for reasons out of scope for this question, but it is a necessity), I know I have to have a click handler set up as so:
$('.elementToInsertTo').on('click', '.add2CartLink', function() { ... });
Where '.elementToInsertTo' is the parent element that is NOT dynamically created, and is present on the page at page load. There are multiple of these parents, hence why I can't use an element ID. Don't think it makes a difference though.
Again, I can confirm that the function call in this click listener works everywhere except Android phones (as far as I can tell). Any idea why this may be? I've read StackOverflow pages all day, but nothing seems related to this. I've read a bunch about JS closures (which may still be the issue) and the like, but none of that seems to be relevant since the link click listener is working on most all devices I have tested on (even the Android tablet's Chrome browser, which is the part that really is confusing to me).
If you happen to have seen this issue before or have any idea why this may be happening, please write it out before reading the next part, so as not to confuse or bias you.
Ok, now to the part that is even more mind-boggling, though I hope this only helps figure this out and doesn't confuse the situation.. I connected one of the phones to my computer with a USB and did some remote debugging using Chrome developer tools as described here (https://developers.google.com/chrome-developer-tools/docs/remote-debugging). I could confirm there that the click listeners were not working (they weren't being triggered)... (and now here comes the crazy part) UNTIL I did some element inspection on the link (i.e. the link was highlighted on my phone as I was inspecting the DOM-element in my browser, again using Chrome dev tools) and then clicked the link. This made it so that the click listener worked! What?? To debug further, if I inspected any of the DOM elements on the page and clicked the link, the click listener worked. If I changed tabs away from the dev tools tab, or simply stopped inspecting the DOM elements in Chrome Dev tools, the link click listener no longer worked. I really don't know what to make of this, but I'm hoping this part of information narrows down what may be going on with the Android phones and the click listeners.
Happy to try to provide any other info I can, though I am without the Android phone for testing at the moment.
Thanks!

Tap was still needed (thanks for both suggestions), but the issue was with a 3rd party JS library stopPropogation() call. Apparently this only happened on Android phones, but regardless, after removing the line, the click (on computers) and tap (on mobile) now works everywhere. Thanks!

How do I disable body.blur() in IE8?

I work on an enterprise web application that runs in IE8. It appears blur() is being called on the body causing the IE window to be sent to the background. Unfortunately this code is in a portion of the application that is controlled by the vendor.
Is there any possible way to prevent blur() from being called on the body without modifying the code that is actually calling body.blur()?
Since this is an enterprise application, solutions outside of changes in the application itself are acceptable; Such as changes to IE8 settings, registry, etc.

You should be able to hard code blur to a dummy method. If you can get in before it is called, just call body.blur = function() {}; (assuming body is pointing to your DOM body element).

Using jQuery you could simply block the event :
$('body').blur(function(e) { e.preventDefault(); });

If using Firefox is an option, i have two answers where i propose replacing the function using Greasemonkey.
Using javascript to create a keylistener hotkey for facebook page "like"
Greasemonkey script to replace jQuery plugin function?
If you have to use IE, you might need to change the page itself.
(I know there is Trixie and IE7pro for IE, but never used).

I had an issue when using javaScript editor:CLEditor, if I use jQuery blur() method on it, the IE window goes to the background. CLEditor has it's iframe which has its own body. When you extract that body and use body.blur(), IE browser will go to the background.
Other browsers are not showing that behavior, so it is better to use FF, or Chrome if you are experiencing this.
If you remove body.blur(), probably you would have less problems with IE than you have now, but still you could experience some minor bugs (something is not loosing focus at certain point), but I suppose you could live with it. However if blur() event is enriched with some logic, it could be problem - then find its definition and move logic to some other event that is started with the browser (onload, or ready).

document.body.blur=function(){document.body.focus()}

Safari 5.1 broke HTML native drag and drop?

Last night, I thought I'd do a quick project to demonstrate HTML5 capabilities and to try some things out. However, I can't seem to figure out how to get drag and drop to work in Safari, while it works perfectly in Chrome and Firefox. More precisely, it seems that drop event does not fire in Safari, when you try to drag an image inside the website into the drop area. At the same time it does fire when you drag and drop a file from desktop.
I'm not really sure, but I'm pretty certain that when I tried the same script at work (where I have Safari 5.0.2 etc), it fired the drop event (going to check it tomorrow to be sure) and gave me the FileReader-related errors that were expected. But when I just installed Safari 5.1 on my own PC, I only get dragover, enter and leave events (and drop too if the file was dragged into the browser).
I've been Googling for some time now and don't seem to find a single example of drag and drop that actually works in Safari 5.1. Even Safari's dev-centre's sample doesn't work, let alone html5demo.com 1 and html5demo.com 2. This leads me to think whether the Safari has a bug, or maybe they have implemented something mandatory that isn't reflected in the dev-centre (last updated in 2009).
The script I'm trying to fix is at my site (sorry guys, no problem specific code to post, as it seems to be broken elsewhere too).
PS! I might have introduced some bugs into my own site while desperately trying to fix the drag and drop in Safari, but I'm too tired to fix them right now.
UPDATE: Just confirmed at work that the drop event does fire in Safari 5.0.2 on Mac OS X.
UPDATE 2: Also confirmed that everything works perfectly fine with Safari 5.0.6 on Win 7, the same computer that fails with 5.1

Testing with Safari 5.1.7 Mac:
To see the drop event fire, you have to handle the dragover event and call event.preventDefault().
Here's the (quite entertaining) discussion where I found the answer:
http://www.quirksmode.org/blog/archives/2009/09/the_html5_drag.html
I don't know if this really solves the question because the asker's site (at least as of today) does this. It works fine on my machine (as do the HTML5 demo pages). But this may help someone coming to this thread with this problem who doesn't know about this rather unintuitive implementation detail.

I am using Safari 5.1.5 (7534.55.3) on a Windows 7 PC which I just installed the other day, no previous installs of Safari and I cannot get any of the online HTML5 drag-n-drop demos to work.
I am working on a project with drag-n-drop and Modernizr tells me that I'm good to go with Safari (Modernizr.draganddrop == true), but when I actually drop the item the drop event does not fire.
I've added alert debugging and nothing.
My testing shows that Safari 5.1.5 (7534.55.3) on a Windows 7 PC drop event is broken. All other drag events seem to work: dragstart, dragend, dragenter, dragleave, dragover.

Just to clarify: Visited your site and found no errors. Opened the console, no error, and everything appeared to function as designed. Tried all provided examples with no error.
All examples work fine Safari Version 5.1 (7534.48.3). Sorry, mate – Maybe it's a setting you've changed?
Allow me to suggest a possibility:
Go to Safari->Empty Cache... Then Safari->Reset Safari... Try reloading the page.
Likely, there's something cached that's creating a conflict. There seems to be nothing wrong with your script in the slightest.
Edit
Some things to check...
Are any of your function names containing reserved words? I've done this, had it not throw any errors, but it simply wouldn't work.
I've had some weird issues with Safari not running methods written as funcName = function(){}. If you can pin down the method that isn't firing (I add a little function when I'm developing called DBG which I'll add below – basically, if a debug flag is set, you log to the console), you can try rewriting the function.
// Some sort of boolean flag.
var debug = true;
// This is kind of an obvious function, but can be expanded as you like.
// Little tricks to make life easier.
function DBG(str) {
debug ? console.log(str) : return;
}
I still think ultimately this boils down to something caching wrong, but it's worth a try.

I encountered similar issues, the drop event appeared to not be firing. Safari apparently expects the "dragover" event to also be bound. As soon as I also added that, it worked. So ... I'm sharing in case it's relevant.
My first attempt:
$(document).bind
drop: (e) ->
// This never gets fired in safari (does work in chrome)
console.log e.originalEvent.dataTransfer.files
false
My "fix":
$(document).bind
dragover: (e) ->
console.log e
false
drop: (e) ->
// This does get fired (in chrome and safari)
console.log e.originalEvent.dataTransfer.files
false

How to debug JAVASCRIPT events? Or how to make all functions call trace?

For example there is a button. It is wrapped by <div>.
When pressing to this button, there is Javascript function call happen, then another function, then calling by ajax to the server and if it's OK, Javascript redirecting this page to another page.
It's hard to debug.
Is it possible to "catch" this event? I.e. to know, what function is called after the click on the button? Button doesn't have attribute onclick i.e. event listener is connected in Javascript.
And if it's not possible then is it possible to make trace? That is to look at all functions calls, which is called after which?
It would be better in visual way, though in textual is also good:)

Yeah - this sort of thing is not as simple as you would like.
Google Chrome, Edge and Opera have an Event Listeners panel. Right-click your button, then select Inspect Element. Make sure the correct element is selected, then check the Event Listeners panel on the right.
In Firefox this feature is implemented differently:
The inspector shows the word “event” next to elements in the HTML
Pane, that have event listeners bound to them. Click the icon, then
you’ll see a popup listing all the event listeners bound to this
element.
You can also use the debugger keyword to set a breakpoint in the call stack somewhere. Then use your favorite javascript debugger (built-in dev tools in Safari, Google Chrome & IE8, firebug for Firefox). In each of these, there's a call stack that'll allow you to navigate through the current call stack.

You can use firebug to trace the javascript code. Its plugin of Firefox to trace the styles (css), js and also allows to edit.
Opera provides dragonfly which is similar to firebug

Besides the accepted answer (upvoted) which mentions the event listeners available on the developer tools, I want to emphasize a simple, yet potentially useful point. If the expected event does not appear on the list, as expected, an alternative to a debugger is good plain old console.log() to find out what's going on.
As a practical example, it helped me to literally see the cause of the issue, when I logged the relevant element.innerHTML at the right place. Particularly helpful after changes to the DOM.

Check out the debugging features in Firebug, it'll let you add JavaScript breakpoints and step through your code.