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Possible to use CSS transitions with textarea rows value?

In all the years I've been developing websites this situation has never cropped up before and I'm not sure that what I'm attempting to do is even possible.
I have a React component with a textarea. It's initial state is rendered with a height of 1 row like this :
state = {
rows: 1
}
...
<textarea
...
rows={this.state.rows ? this.state.rows : 1}
onFocus={this.onFocus}
...
/>
The onFocus function changes the rows state to 5, thereby expanding the textarea.
This works perfectly, but I'm now trying to add CSS transitions to the textarea so it expands nicely instead of just instantly expanding.
Everything I've tried doesn't work, for example :
textarea#content {
transition: all 2s ease-in-out;
}
...so my question is - is it not possible to use CSS transitions in this way? I did some googling and couldn't find any answers which leads me to believe that it isn't, but I just want to make sure before I set about achieving this another way.

Can't say how React might be involved here, but for a transition to work, the CSS property being transitioned must have a default value set for it. You are indirectly affecting the height property by changing the rows, but you are not actually specifying that you want the height to change, so you can't transition the height if you are only indirectly changing it. Also, there is no CSS rows property, so no luck on transitioning that either.
The solution is to not set the height indirectly with rows in the first place. Set the height directly and set a default value for height in the CSS.
And, you really don't even need JavaScript to do this:
textarea {
height:1em; /* Initial value required for transitions to work */
transition:height 1s ease-in-out; /* configure the transition*/
}
/* Style to be applied automatically when the textarea recievs the focus */
textarea:focus {
height:5em; /* A change in this property will trigger the transition */
}
<textarea></textarea>

css3 transition on background image doesn't work in Firefox

This is a follow up to my question here: jquery UI add class with animation does't work
See the new jsfiddle and try this in Firefox: http://jsfiddle.net/40mga4vy/3/
-webkit-transition: all 2.0s ease;
-moz-transition: all 2.0s ease;
-o-transition: all 2.0s ease;
transition: all 2.0s ease;
This code in combination with some jquery animates a background image change when selecting a new background image from a select-element. It works in all browsers except Firefox (tested in MacOS 35.0.1).
While animating a change in the background color and width/height properties works like a charme in FF: http://jsfiddle.net/tw16/JfK6N/ - animating a background image does not work.
Researching showed that a "left" property has to be set but it turned out to not have any impact. I also tried various notations but with no success, I cannot make it work.
There is a workaround shown in this fiddle:
http://jsfiddle.net/40mga4vy/1/
function changeBackground() {
$('#wallpaper').removeClass();
$("#wallpaper").addClass("wallpaper_" + $("#select_category").val()).css('opacity','0').animate({opacity:'1'});
};
This works in FF but its a bit ugly as the class is removed and then opacity raises afterwards (doesn't look as smooth as the css solution).
Any hints/tricks or is this simply not supported?

As far as I know, there is no suport in any browser to swap images smoothly in one single element in css.
After you do what you need, make sure you take a look into performance, your workaround is not as much as efficient as it could. In this code
$("#wallpaper").addClass("wallpaper_" + $("#select_category").val()).css('opacity','0').animate({opacity:'1'});,
the browser will take every single step until
.animate({opacity:'1'}).
For instance, the browser first has to find $("#wallpaper") then, it will call for .addClass("wallpaper_" + ...);
and concatenate the result from finding $("#select_category") then getting .val() and so on. everytime this function is called, it will iterate through every single of these objects, so it is not as efficient as probably could and with two more animations in the page, it may became a bit laggy, if possible, use animations through CSS.
Anyway, what I sugest you to do is (if i'm right about what you want), just do what's in here https://jsfiddle.net/bmjg5g9s/

How to correctly wait until JavaScript applies inline Css

I have this jsFiddle. When the button is clicked, I want to put the red div behind the black one immediately, then start the animation.
var red = document.getElementById("red");
var button = document.getElementById("button");
button.addEventListener("click",function () {
red.style.zIndex = -1;
red.classList.remove("shifted");
});
However, as you can see, they seem to be occurring as two separate actions. I know I can use setTimeout to wait until the zIndex property is applied, but I do not know how long I am supposed to wait, and the duration perhaps differs from browsers to computers.
Should I create a loop that will check if zindex was applied? But this also sounds like an unintelligent solution. What is the correct way?
EDIT: I do not want to change the zIndex on the black div.

You can bind to the transitioned state of the element, something like this:
("#mySelector").bind("transitionend", function(){ 'yourcodehere' });
Also, here is some info on it:
https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Using_CSS_transitions
https://developer.mozilla.org/en-US/docs/Web/Reference/Events/transitionend
Without jQuery:
el.addEventListener("transitionend", updateTransition, true);
Edit:
There was some confusion as to the usage of:
-webkit-transition-duration: 1s;
This is applied like a styling as well. So anytime you make alterations to the element it is on, you are triggering this. You have TWO transition calls, one for setting the z-index, another for the movement.

Just put a
-webkit-transition-property: -webkit-transform;
into the #red and everything is fine. ;) This applies the transition only to specified property.
JSFIDDLE: http://jsfiddle.net/Qvh7G/.

The problem is with zIndex - the transform time delays the change in the zIndex.
You can simply force the duration for the transform property.
Replace:
-webkit-transition-duration: 1s;
With
-webkit-transition: -webkit-transform 1s; // ease-in;

Does jQuery animate between two different CSS classes?

I am trying to understand how jQuery animations work.
For instance, if I have an a element with CSS that makes it look like a clickable image and a given with and height in CSS, how would I safely animate the width and height of this element?
Do I need to animate the values in the CSS class? Or do I need to set a new CSS class with the target values for width and height, and let jQuery animate from oldClass to newClass?
Or can I simply use the .width() and .height() methods of jQuery, regardless of what values are specified in CSS?
What confuses me is: If I tweak the width of an element with jQuery, does this also modify my CSS, or does jQuery / JavaScript simply override the specified values in CSS with something else? I mean: After use jQuery to edit the width, does this width become the new value in the CSS file as well? Can I apply this class to other elements and they will have the new width?

It will overide inline style.
I will now show a version with top, left being animated but you can apply it on almost all CSS properties.
HTML
<span id="test">blablabla</span>
CSS
span{
position:absolute;
display:block;
height:50px;
width:50px;
}
jquery
$('#test').animate({top:'100px',left:'50px'}, 500);
fiddle

I know it's been a long time, but it may help someone looking for the answer anyway. Relying on CSS3 transition property can lead to trouble when wanting to support older browsers.
The requested behaviour of animating between two states (CSS Classes) can fully be accomplished by using jQuery UI, which supports this by extending the switchClass() method. It also supports all the perks of the animate() method, such as duration, easing, callback, etc.
As the official documentation states: '
Similar to native CSS transitions, jQuery UI's class animations
provide a smooth transition from one state to another while allowing
you to keep all the details about which styles to change in CSS and
out of your JavaScript.
You can read all about it here.
jQuery UI can also be compiled to include only the things you need, so you can reduce the size of the library by excluding the features you won't use. Check the available options here.
Hope it helped someone!

jQuery animate only animates numeric css values. It will not animate between classes (see example below for how to do that). The .animate() function adds the css you give it as a paramater and adds it as inline css. It will always override your stylesheet css. This is fine but a little messy and can get out of control very easily.
However, if you want to animate between classes, it is better for performance and cleaner to use css3 transition property. See example:
HTML
<div class="myTestAnimation">Something to test</div>
JQuery (could use vanilla javascript for this as well). Just toggling between classes. This way you don't have any styling info in your css at all.
jQuery(document).ready(function($) {
$(".myTestAnimation").click(function() {
$(this).toggleClass("animate");
});
});
CSS (this animates the width and height and background color) .animate() will not animate background color so that is an added bonus.
.myTestAnimation {
width: 50px;
height: 50px;
background-color: red;
-webkit-transition: background-color 300ms linear, width 300ms linear, height 300ms linear;
transition: background-color 300ms linear, width 300ms linear, height 300ms linear;
position: relative;
}
.myTestAnimation.animate {
background-color: blue;
width: 200px;
height: 200px;
}

What is the cleanest way to disable CSS transition effects temporarily?

I have a DOM element with this effect applied:
#elem {
transition: height 0.4s ease;
}
I am writing a jQuery plugin that is resizing this element, I need to disable these effects temporarily so I can resize it smoothly.
What is the most elegant way of disabling these effects temporarily (and then re-enabling them), given they may be applied from parents or may not be applied at all.

Short Answer
Use this CSS:
.notransition {
-webkit-transition: none !important;
-moz-transition: none !important;
-o-transition: none !important;
transition: none !important;
}
Plus either this JS (without jQuery)...
someElement.classList.add('notransition'); // Disable transitions
doWhateverCssChangesYouWant(someElement);
someElement.offsetHeight; // Trigger a reflow, flushing the CSS changes
someElement.classList.remove('notransition'); // Re-enable transitions
Or this JS with jQuery...
$someElement.addClass('notransition'); // Disable transitions
doWhateverCssChangesYouWant($someElement);
$someElement[0].offsetHeight; // Trigger a reflow, flushing the CSS changes
$someElement.removeClass('notransition'); // Re-enable transitions
... or equivalent code using whatever other library or framework you're working with.
Explanation
This is actually a fairly subtle problem.
First up, you probably want to create a 'notransition' class that you can apply to elements to set their *-transition CSS attributes to none. For instance:
.notransition {
-webkit-transition: none !important;
-moz-transition: none !important;
-o-transition: none !important;
transition: none !important;
}
Some minor remarks on the CSS before moving on:
These days you may not want to bother with the vendor-prefixed properties like -webkit-transition, or may have a CSS preprocessor that will add them for you. Specifying them manually was the right thing to do for most webapps when I first posted this answer in 2013, but as of 2023, per https://caniuse.com/mdn-css_properties_transition, only about 0.4% of users in the world are still using a browser that supports only a vendor-prefixed version of transition.
There's no such thing as -ms-transition. The first version of Internet Explorer to support transitions at all was IE 10, which supported them unprefixed.
This answer assumes that !important is enough to let this rule override your existing styles. But if you're already using !important on some of your transition rules, that might not work. In that case, you might need to instead do someElement.style.setProperty("transition", "none", "important") to disable the transitions (and figure out yourself how to revert that change).
Anyway, when you come to try and use this class, you'll run into a trap. The trap is that code like this won't work the way you might naively expect:
// Don't do things this way! It doesn't work!
someElement.classList.add('notransition')
someElement.style.height = '50px' // just an example; could be any CSS change
someElement.classList.remove('notransition')
Naively, you might think that the change in height won't be animated, because it happens while the 'notransition' class is applied. In reality, though, it will be animated, at least in all modern browsers I've tried. The problem is that the browser is buffering the styling changes that it needs to make until the JavaScript has finished executing, and then making all the changes in a single "reflow". As a result, it does a reflow where there is no net change to whether or not transitions are enabled, but there is a net change to the height. Consequently, it animates the height change.
You might think a reasonable and clean way to get around this would be to wrap the removal of the 'notransition' class in a 1ms timeout, like this:
// Don't do things this way! It STILL doesn't work!
someElement.classList.add('notransition')
someElement.style.height = '50px' // just an example; could be any CSS change
setTimeout(function () {someElement.classList.remove('notransition')}, 1);
but this doesn't reliably work either. I wasn't able to make the above code break in WebKit browsers, but on Firefox (on both slow and fast machines) you'll sometimes (seemingly at random) get the same behaviour as using the naive approach. I guess the reason for this is that it's possible for the JavaScript execution to be slow enough that the timeout function is waiting to execute by the time the browser is idle and would otherwise be thinking about doing an opportunistic reflow, and if that scenario happens, Firefox executes the queued function before the reflow.
The only solution I've found to the problem is to force a reflow of the element, flushing the CSS changes made to it, before removing the 'notransition' class. There are various ways to do this - see here for some. The closest thing there is to a 'standard' way of doing this is to read the offsetHeight property of the element.
One solution that actually works, then, is
someElement.classList.add('notransition'); // Disable transitions
doWhateverCssChangesYouWant(someElement);
someElement.offsetHeight; // Trigger a reflow, flushing the CSS changes
someElement.classList.remove('notransition'); // Re-enable transitions
Here's a JS fiddle that illustrates the three possible approaches I've described here (both the one successful approach and the two unsuccessful ones):
http://jsfiddle.net/2uVAA/131/

Add an additional CSS class that blocks the transition, and then remove it to return to the previous state. This make both CSS and JQuery code short, simple and well understandable.
CSS:
.notransition {
transition: none !important;
}
Note: !important was added to be sure that this rule will have higher preference, because using an ID is more specific than class.
JQuery:
$('#elem').addClass('notransition'); // to remove transition
$('#elem').removeClass('notransition'); // to return to previouse transition

I would advocate disabling animation as suggested by DaneSoul, but making the switch global:
/*kill the transitions on any descendant elements of .notransition*/
.notransition * {
transition: none !important;
}
.notransition can be then applied to the body element, effectively overriding any transition animation on the page:
$('body').toggleClass('notransition');

For a pure JS solution (no CSS classes), just set the transition to 'none'. To restore the transition as specified in the CSS, set the transition to an empty string.
// Remove the transition
elem.style.transition = 'none';
// Restore the transition
elem.style.transition = '';
If you're using vendor prefixes, you'll need to set those too.
elem.style.webkitTransition = 'none'

You can disable animation, transition, transforms for all of element in page with this CSS code:
var style = document.createElement('style');
style.type = 'text/css';
style.innerHTML = '* {' +
' transition-property: none !important;' +
' transform: none !important;' +
' animation: none !important;}';
document.getElementsByTagName('head')[0].appendChild(style);

I think you could create a separate CSS class that you can use in these cases:
.disable-transition {
transition: none;
}
Then in jQuery you would toggle the class like so:
$('#<your-element>').addClass('disable-transition');

If you want a simple no-jquery solution to prevent all transitions:
Add this CSS:
body.no-transition * {
transition: none !important;
}
And then in your js:
document.body.classList.add("no-transition");
// do your work, and then either immediately remove the class:
document.body.classList.remove("no-transition");
// or, if browser rendering takes longer and you need to wait until a paint or two:
setTimeout(() => document.body.classList.remove("no-transition"), 1);
// (try changing 1 to a larger value if the transition is still applying)

This is the workaround that worked easily for me. It isn't direct answer to the question but still may help someone.
Rather than creating notransition class which was supposed to cancel the transition
.notransition {
-webkit-transition: none !important;
-moz-transition: none !important;
-o-transition: none !important;
transition: none !important;
}
I created moveTransition class
.moveTransition {
-webkit-transition: left 3s, top 3s;
-moz-transition: left 3s, top 3s;
-o-transition: left 3s, top 3s;
transition: left 3s, top 3s;
}
Then I added this class to element with js
element.classList.add("moveTransition")
And later in setTimeout, I removed it
element.classList.remove("moveTransition")
I wasn't able to test it in different browsers but in chrome it works perfectly

If you want to remove CSS transitions, transformations and animations from the current webpage you can just execute this little script I wrote (inside your browsers console):
let filePath = "https://dl.dropboxusercontent.com/s/ep1nzckmvgjq7jr/remove_transitions_from_page.css";
let html = `<link rel="stylesheet" type="text/css" href="${filePath}">`;
document.querySelector("html > head").insertAdjacentHTML("beforeend", html);
It uses vanillaJS to load this css-file. Heres also a github repo in case you want to use this in the context of a scraper (Ruby-Selenium): remove-CSS-animations-repo

does
$('#elem').css('-webkit-transition','none !important');
in your js kill it?
obviously repeat for each.

I'd have a class in your CSS like this:
.no-transition {
-webkit-transition: none;
-moz-transition: none;
-o-transition: none;
-ms-transition: none;
transition: none;
}
and then in your jQuery:
$('#elem').addClass('no-transition'); //will disable it
$('#elem').removeClass('no-transition'); //will enable it