But binding an animation to a dynamically added element makes the animation restart from 0% every time the element is replaced.

A partial solution is binding the animation to an unmutable parent element. The animation then will run continuously and affect any child elements, even if they are dynamically replaced.

But this solution is limited in that I cannot select which animations are inherited by which child element.

For this code:

HTML

<div class='parent'>
  <div class='child one'>Some text</div>
  <div class='child two'>Other text</div>
</div>

CSS (SASS)

.parent
  animation: BY 15s infinite alternate

.child.two
  animation: RG 15s infinite alternate

@keyframes BY
  0%
    color: blue
  100%
    color: yellow

@keyframes RG
  0%
    color: red
  100%
    color: green

Only the BY animation from '.parent' which affects '.child.one' text remains continous across any dynamic replacement of '.child.one'. While the animation of '.child.two' restarts at 0% every time it is dynamically replaced.

This is a codepen illustrating this behaviour: https://codepen.io/plagasul/pen/WNerBvO

I would like '.child.one' and '.child.two' to have different animations, that are both continuous across dynamic replacement of these elements.

Thank you

This seems like a problem that might not be solvable with CSS alone. If I understand correctly you want the animation, of the child that is replaced by another child, to start at the point where it the previous animation ended.

You could look into the Web Animations API. As of this moment browser support is not great, but might get better in the future.

It does, however, have the capabilities that you are looking for. As referenced in this article on MDN, it is possible to get the point in time of your animation where it should start from by using the currentTime property of an animation.

// Just like with CSS we use keyframes to create an animation.
const keyframes = [
    { 
        color: 'blue' 
    },
    { 
        color: 'yellow' 
    }
];

// Set the timing properties of the animation just like you have in CSS.
const timing = {
    duration: 15000,
    direction: 'alternate',
    iterations: Infinity,
};

// And add it all together.
const currentAnimation = document.querySelector('.child').animate(keyframes, timing);

The code here is the JavaScript equivalent of CSS animations. The color of the .child class will change for as long as the element exists, just like in CSS.

Before you replace a child with a new one you'll want to know where the animation is in terms of time. Get it by accessing the currentTime property as mentioned before.

// Returns the position in time of the animation in milliseconds.
const position = currentAnimation.currentTime;

So now you have the position of the animation. You can use it to set the starting point of the animation on the new element. Just like this:

// Create a new animation
const newAnimation = docum... // You know the drill.

// Update the currentTime with the position of the previous animation.
newAnimation.currentTime = position;

The new animation will start on the position that we stored.

You still need to wrap these examples into functions to use them in your code, but I hope you can figure that out. If the Web Animations API is not something you could use then look for a framework with better support, like GreenSock or AnimeJS. This article also has a list of good alternatives.

Hope this helps and have a nice day!

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