Как изменить скорость анимации css

It’s a very difficult process to do so. Currently the only way to change an animation mid-animation is to use a setInterval to approximate the current keyframes percentage, save the properties of that keyframe, update the animation (in your case just the speed) then apply the new version of the animation starting from the saved point. I created a similar example in the article I wrote for CSS Tricks called Controlling CSS Animations & Transitions with Javascript

As the article described, it’d be easier to change the speed on animationIteration, in your case that would look like this demo, but it is still far from pretty

 var pfx = ["webkit", "moz", "MS", "o", ""],
    rotates = $('.rotate'),
    prevent = false;

function PrefixedEvent(element, type, callback) {
    for (var p = 0; p < pfx.length; p++) {
        if (!pfx[p]) type = type.toLowerCase();
        element.addEventListener(pfx[p]+type, callback, false);
    }
}

function listen() {
    for(var i = 0, j = rotates.length; i < j; i ++) {
        PrefixedEvent(rotates[i], "AnimationIteration", function() {
            if(!$('#faster').is(':checked') && !prevent) {
                var el = $(this),  
                   newOne = el.clone(true)
                            .css({'animation':'rotate 2s linear infinite'});
                el.before(newOne);        
                $("." + el.attr("class") + ":last").remove();
                rotates = $('.rotate');
                listen();
                prevent = true;
            }
            else if($('#faster').is(':checked') && prevent) {
                prevent = false;
                var el = $(this),
                   newOne = el.clone(true)
                            .css({'animation':'rotate 1.5s linear infinite'});
                el.before(newOne);
                $("." + el.attr("class") + ":last").remove();
                rotates = $('.rotate');
                listen();
            }
        });
    }
}
listen();

At the moment we cannot simply restart the animation with a different timing function (even if you pause it and run it again like Michael said). As a result you either have to use a setInterval (which gives a higher delay) or clone the element with the changed values. For more information on the approach I used look at the demo, I added comments to all the javascript I added

EDIT based on your linked fiddle in comments

Since you’re trying to simulate a roulette, you don’t need to use javascript at all! Simply change your rotation animation to change speed over time (: Here’s an rough version of how you’d do so, but you should add more keyframes to make it appear more smooth than it currently behaves

@-webkit-keyframes rotate {
    0%   { -webkit-transform: rotate(   0deg); }
    30%  { -webkit-transform: rotate(2600deg); }
    60%  { -webkit-transform: rotate(4000deg); }
    80%  { -webkit-transform: rotate(4500deg); }
    100% { -webkit-transform: rotate(4780deg); }
}

EDIT 2

Since you need apparently need have a random ending position and likely run it multiple times you can do something like this which is much simpler, only uses CSS transforms, and incredibly useful

var img = document.querySelector('img');
img.addEventListener('click', onClick, false);    
var deg = 0;

function onClick() {
    this.removeAttribute('style');        
    deg += 5 * Math.abs(Math.round(Math.random() * 500));        
    var css = '-webkit-transform: rotate(' + deg + 'deg);';        
    this.setAttribute(
        'style', css
    );
}

and the CSS

img { -webkit-transition: -webkit-transform 2s ease-out; }

Edit 3

This isn’t fully relevant or irrelevant, but you can do very similar things using GSAP like I did in this project to make it more interactive/dynamic

I have searched through a lot of questions related to my question in stackoverflow but i haven’t found one yet that answers my question with plain JavaScript (not using libraries of any kind).

My problem is that I have an infinite animation with CSS3 i.e.:

.clockwiseAnimation {
    top: 270px;
    left: 200px;
    position: absolute;

    -webkit-animation: clockwise 4s linear infinite; /* Chrome, Safari 5 */
    -moz-animation: clockwise 4s linear infinite; /* Firefox 5-15 */
    -o-animation: clockwise 4s linear infinite; /* Opera 12+ */
    animation: clockwise 4s linear infinite; /* Chrome, Firefox 16+, IE 10+, Safari 5 */
}
@-webkit-keyframes clockwise {
    from { -webkit-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -webkit-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@-moz-keyframes clockwise {
    from { -moz-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -moz-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@-o-keyframes clockwise {
    from { -o-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -o-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@keyframes clockwise {
    from { transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}

This animation allows me to spin (clockwise) whatever tag that has the class «clockwiseAnimation».

What I want to do is to change the time of execution (I’ll call it speed) of the animation with javascript like:

HTML:

<span id="someID" class="clockwiseAnimation">sometext</span>

JavaScript:

var style = document.getElementById("someID").style,
speed = 6; 
//obviously the speed is dynamic within my site (through an `<input type="range">`)
//for the purposes of this example I set the speed to a different value(6seconds) than the original value(4seconds).
style.webkitAnimationDuration = style.mozAnimationDuration = style.oAnimationDuration = style.animationDuration = speed + "s";

It works when I pause and then play(by play I mean UNPAUSE not restart) the animation, i.e.:

var style = document.getElementById("someID").style;
some = 6; //it is dynamic (as I pointed out before)

//pause
style.webkitAnimationPlayState = style.mozAnimationPlayState = style.oAnimationPlayState = style.animationPlayState = "paused";

//change speed
style.webkitAnimationDuration = style.mozAnimationDuration = style.oAnimationDuration = style.animationDuration = speed + "s";  

//play (== UNPAUSE) //UPDATE: Added the timeout because I can't get it to work any other way.
setTimeout(function(){
            style.webkitAnimationPlayState = style.mozAnimationPlayState = style.oAnimationPlayState = style.animationPlayState = "running";
        },1);

UPDATED:

And it works! BUT, it has a big RANDOM jump in the animation, meaning that when I change the «speed» with the «<input type="range"> slider» the element jumps to a random location (not the beginning nor the end of the animation just a random location).

NOTE: Pause and play works very smooth without changing the «speed» of the animation.

My question(s): Can I change the «speed» of the animation smoothly WITH JavaScript? (WITHOUT the jumping)
If the answer is: «There is not a way to do it smoothly throughout the animation execution», then:
Is there a way to change it in the next iteration of the infinite animation?
If so:
Then how can I tell it to start in the next iteration and how to know which is the next iteration if I set the animation to infinite (animation-iteration-count property of the element that is doing the animation always returns «infinite»).

Here is an example. I hope it helps.

I have searched through a lot of questions related to my question in stackoverflow but i haven’t found one yet that answers my question with plain JavaScript (not using libraries of any kind).

My problem is that I have an infinite animation with CSS3 i.e.:

.clockwiseAnimation {
    top: 270px;
    left: 200px;
    position: absolute;

    -webkit-animation: clockwise 4s linear infinite; /* Chrome, Safari 5 */
    -moz-animation: clockwise 4s linear infinite; /* Firefox 5-15 */
    -o-animation: clockwise 4s linear infinite; /* Opera 12+ */
    animation: clockwise 4s linear infinite; /* Chrome, Firefox 16+, IE 10+, Safari 5 */
}
@-webkit-keyframes clockwise {
    from { -webkit-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -webkit-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@-moz-keyframes clockwise {
    from { -moz-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -moz-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@-o-keyframes clockwise {
    from { -o-transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { -o-transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}
@keyframes clockwise {
    from { transform: rotate(0deg) translateX(150px) rotate(0deg); }
    to { transform: rotate(360deg) translateX(150px) rotate(-360deg); }
}

This animation allows me to spin (clockwise) whatever tag that has the class «clockwiseAnimation».

What I want to do is to change the time of execution (I’ll call it speed) of the animation with javascript like:

HTML:

<span id="someID" class="clockwiseAnimation">sometext</span>

JavaScript:

var style = document.getElementById("someID").style,
speed = 6; 
//obviously the speed is dynamic within my site (through an `<input type="range">`)
//for the purposes of this example I set the speed to a different value(6seconds) than the original value(4seconds).
style.webkitAnimationDuration = style.mozAnimationDuration = style.oAnimationDuration = style.animationDuration = speed + "s";

It works when I pause and then play(by play I mean UNPAUSE not restart) the animation, i.e.:

var style = document.getElementById("someID").style;
some = 6; //it is dynamic (as I pointed out before)

//pause
style.webkitAnimationPlayState = style.mozAnimationPlayState = style.oAnimationPlayState = style.animationPlayState = "paused";

//change speed
style.webkitAnimationDuration = style.mozAnimationDuration = style.oAnimationDuration = style.animationDuration = speed + "s";  

//play (== UNPAUSE) //UPDATE: Added the timeout because I can't get it to work any other way.
setTimeout(function(){
            style.webkitAnimationPlayState = style.mozAnimationPlayState = style.oAnimationPlayState = style.animationPlayState = "running";
        },1);

UPDATED:

And it works! BUT, it has a big RANDOM jump in the animation, meaning that when I change the «speed» with the «<input type="range"> slider» the element jumps to a random location (not the beginning nor the end of the animation just a random location).

NOTE: Pause and play works very smooth without changing the «speed» of the animation.

My question(s): Can I change the «speed» of the animation smoothly WITH JavaScript? (WITHOUT the jumping)
If the answer is: «There is not a way to do it smoothly throughout the animation execution», then:
Is there a way to change it in the next iteration of the infinite animation?
If so:
Then how can I tell it to start in the next iteration and how to know which is the next iteration if I set the animation to infinite (animation-iteration-count property of the element that is doing the animation always returns «infinite»).

Here is an example. I hope it helps.