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Pause a javascript

I'm looking for a chrome feature similar to debugger/breakpoint that lets me pause a script.
Why. I like to test some css in chrome-inspector. Since it's a loading spinner it will only be visible for some milliseconds. That time is to short to play with css ;)
Why not breakpoint...
Because chrome covers the entire page with a black layer so I cannot right-click and inspect a DOM-element as I like.
So is it possible to get rid of the black layer chrome has in debegger mode? or can I simply pause a script, play around with the css and the play it again.
Thanx in advance.

In your Javascript, you can simply write:
console.log(element);
debugger;
When the Chrome developer tools console is open, this line will pause your script without placing a breakpoint manually. console.log(element); will let you access the element you wish to debug or modify via the console.
After the script stops, you can use the DOM explorer, select your element, and in the DOM properties window, under "Styles", change its display property to none to make it disappear.

I found an ok answer to my own question. Simply use the select-element tool in chrome rather than right click.
Icon to the left
It temporary removes the black-layer until the element is selected. But if you want to see the correct colors without the black layer covering it you need to display:none it in the inspector. Also if you want to work on hovers or other similar stats the black layer will prevent hovers and such.

Inspect element that only appear when other element is mouse overed/entered

Often I want to inspect an element (e.g. tooltip) that only appears when another element is mouse overed/entered. The element that appears, is made visible via jQuery's mouseenter event.
I can't inspect the tooltip, since the tooltip disappears when my mouse leaves the containing element.
Is there a way to pause JS events so I could hover on the element, then pause the browser's JS, and successfully inspect it?
For an example, try inspecting Twitter bootstrap's tooltips: http://getbootstrap.com/javascript/#tooltips.

It's fairly easy in Chrome 38.0.2094.0.
Here's what it'll look like:
Step-by-step:
Open the DevTools in the Sources panel
Make the tooltip appear by hovering over the button
Press F8 to freeze the page
Switch to the Elements panel and use the magnifying glass icon in the top left to select the tooltip
If the tooltip shows up because of CSS, here's what you can do in that case:
Step-by-step:
Open the DevTools
Select the triggering element in the dev tools (the link)
Right click, and select "force element state", and select ":hover"
Inspect the CSS tooltip

Both Safari's and Chrome's Web Inspector offers checkboxes where you can toggle the :active, :focus, :hover and :visited state of an element. Using those might be even easier.
Safari:
Chrome:

There's also another tricky way to do it :
Go over the element which makes your tooltip appear.
Right click to open the contextual menu.
Move your mouse to your dev tool window and left click anywhere in the dev tool panel.
Your tooltip will stay visible, you will then be able to inspect it in the Element tab.
Tested on Chrome. Doesn't seem to work on Firefox.

While #SomeGuy's answer is excellent (t-up for animated gifs), as an alternative you can always do it programmatically. Just pop open the console and type in the event name
document.getElementById('id').dispatchEvent(new Event('event-type'));
(with pure javascript specific syntax may vary by browser)
Even easier with jQuery:
$('#id').trigger('event-type');
In your example (http://getbootstrap.com/javascript/#tooltips), open the console and type in, for example:
$("button:contains('Tooltip on right')").mouseenter();
And the tooltip appears in the DOM and can be manually inspected/modified:
<div style="top: 14406.9px; left: 1048.25px; display: block;"
id="tooltip952596" class="tooltip fade right in" role="tooltip">
<div style="" class="tooltip-arrow"></div>
<div class="tooltip-inner">Tooltip on right</div></div>
As in the comments, if you move the mouse pointer over the page frame, you can trigger other events such as mouseout. To prevent this you can press F8 (as in the acc. answer) or type debugger; (which is its script equivalent)

How can I inspect disappearing element in a browser?

How can I inspect an element which disappears when my mouse moves away?
I don't know it's ID, class or anything but want to inspect it.
Solutions I have tried:
Run jQuery selector inside console $('*:contains("some text")') but didn't have any luck mainly because the element is not hidden but probably removed from the DOM tree.
Manually inspecting DOM tree for changes gives me nothing as it seems to be just too fast to notice what have changed.
SUCCESS:
I have been successful with Event breakpoints. Specifically - mousedown in my case. Just go to Sources-> Event Listener Breakpoints-> Mouse-> mousedown in Chrome. After that I clicked the element I wanted to inspect and inside Scope Variables I saw some useful directions.

(This answer only applies to Chrome Developer Tools. See update below.)
Find an element that contains the disappearing element. Right click on the element and apply "Break on... > Subtree Modifications." This will throw a debugger pause before the element disappears, which will allow you to interact with the element in a paused state.
Update Oct 22 2019: with the release of v. 70, it looks like FireFox finally supports this kind of debugging 2 3:
Update Sep 15 2020: Chrome has an "Emulate a focused page" option (you can get it from the [⌘]+[P] Command Menu, or Global Preferences) for this exact need. 5 - h/t #sulco on Twitter

An alternative method in Chrome:
Open devTools (F12).
Select the "Sources" tab.
While the element you want is displayed, press F8 (or Ctrl+/). This will break script execution and "freeze" the DOM exactly as it is displayed.
From this point, use Ctrl+Shift+C to select the element.

Open console
Type in setTimeout(()=>{debugger;},5000);
Press Enter
Now you have 5 seconds to make your element appears. Once it appeared, wait until the debugger hits. As long as you don't resume, you can play with your element and it won't disappear.
Useful tip to avoid repeating those steps above every time:
add this as a bookmarklet:
Bookmark any page
Edit this new bookmark
Replace the URL/location with: javascript:(function(){setTimeout(()=>{debugger;},5000);})();
Next time you wish to use this, just click/tap this bookmark.

Verified in 2022
Do the following:
Open the console and navigate to Elements tab
Type command + shift + P (OSX) or control + shift + P (Windows)
Type the word focused
Select Emulate a focused page from the the menu
Now clicking around in the console will not close the element.

I am using chrome on Mac there I've followed above steps but I'll try to explain a bit more:
Right click and go to inspect element.
Go to sources tab.
Then hover on the element.
Then using keyboard F8 or Command(Window) \. It will pause the screen in a static state and the element won't disappear on hover out.

In Firebug there are different solutions for this:
You can use Break On Mutate inside the HTML panel. (with this you'll also be able to find out which element it is)
You can right-click the element and choose Inspect Element with Firebug
Also you may want to follow issue 551, which asks for a way to temporarily block specific events.
Edit:
To find out which element it is you can also enable the HTML panel options Highlight Changes, Expand Changes and Scroll Changes Into View to make the element visible inside the HTML panel.
Sebastian

In my case, I used Expand recursively option on google chrome:
The steps are:
Inspect the dropdown field
Find the dynamic DOM (the purple highlight)
Right-mouse click on that dynamic DOM
Choose Expand recursively:
We can see all elements are there
Here is a demo:

Hover over the element with your mouse and press F8 (this in Chrome) to pause the script execution. The hover state will remain in visible to you.
It take you to the sources tab.
Go back to Elements tab. This time code will not disapper.

There Could be Dom element and the controller functions fighting at to refresh the session. Running the application by "Start without debugging" helped in my case.
enter image description here

you can view the elements appearing and disappearing in the inspector under elements. If you navigate to the element when it is visible you should be able to see it disappear or see its css change when it status changes.
This is possible with firebug in firefox or the built inspector in chrome.

I've written an article about debugging CSS of disappearing elements
Using hotkeys to automatically go into debugger mode with hotkeys keyboard shortcut:
Install the shortkeys extension
Click on the extension icon and chose "options":
Configure as follows:
Click "Save shortcuts" button (bottom-right)
Now, go to any page, make sure devtools is opened, and hit CTRL+SPACEBAR keys, while your inspection target element is visible.
I'm using Windows OS and this hotkeys combination is good for me and is not "taken" by any other shortcut, but of course, you can choose any other.

i had the same problem but i use Firefox it disappear as soon as i open inspect element found a solution:
open the 4 dashes(settings) go to web developer > Debugger and immediately press F8 which is the shortcut for the pause that stop the script before it kick and detect that you opened the developers tools

Finding out what JS is controlling this

I have a page which is using a nice hover feature which is controlled by javascript, and I was wondering if there is a tool which would tell me what JS is controlling at a specific point as there is a lot of JS files used across the site.

You need a debugging tool, one such tool is mentioned in the comments: Chrome. Once you have the debugger enabled you need to set breakpoints on various events to capture the code flow within all the javascripts. For more info visit here

I would go with Chrome. You can load the page, see all the related JS.
If you are in Chrome, right click on or near the button and click "Inspect Element."
Now you can see all the goodies :)

In google chrome right-click the element, click on "Inspect Element" option. The Chrome Developer window with active Elements tab should appear. You'll see the html structure with your element being highlighted. Right-click on that element and activate all three options in "Break on..." submenu. If some modifications of DOM happen during hover, they will trigger the breakpoint right in the place where you need. But keep in mind, that hover effects can be implemented via css without a bit of javascript, so this plan can fail easily.

As other's have said, use Chrome's web developer toolbar. Go to the sources panel and click the little pause button icon in the lower left corner. This will cause the debugger to activate as soon as the next javascript command is run. Then activate the hover feature - the debugger should pause execution in the callback function that's responsible.
Google actually discusses this exact scenario at the bottom of this documentation page.

How do I find out what javascript runs when I click an element? [duplicate]

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.