Animations are slowing the performance of web page

Question

I have a single page website design in html, javascript and css. There are lots of images on the webpage and all have different-different animation effects according to their categories. I have used wow.js for animation effects on window scroll. While scroll through images, CPU and GPU usage is going very high, due its effect the scrolling is jerky, not smooth. Could anyone please look into this. I have created a codepen example. Please have a look:-

(https://codepen.io/Sny220/pen/jjyEPj)

Code below:-

<!-- HTML -->
<div class="foo foo-text foo-2 col-md-3 col-md-offset-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://www.psychologies.co.uk/sites/default/files/field/image/feelgood%20chemicals.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://kajabi-storefronts-production.global.ssl.fastly.net/kajabi-storefronts-production/blogs/1049/images/BlH7rBrRFGdVF71lofox_TFmaDj07ReWp5C4zcHaw_alex-fergus-look-and-feel-amazing-health-wellness-fat-loss-natural-banner.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-6 col-md-offset-3">
   <div class="inner">
      <h1 class="wow fadeInDown">Hello, world!</h1>
      <p class="wow fadeInUp">Whouaa !!!</p>
   </div>
</div>
<div class="foo foo-3 col-md-6 col-md-offset-3">
   <div class="inner">
      <button type="button" class="btn btn-success">Success</button>
   </div>
</div>
<div class="foo foo-4 col-md-6 col-md-offset-3 wow fadeInDown">
   <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison1.jpg" />
</div>
<div class="foo foo-5 col-md-6 col-md-offset-3">
   <div class="inner">RUBRIQUE 3</div>
</div>
<div data-wow-duration="2s" class="foo foo-1 col-md-3 col-md-offset-3 wow scale-in-ver-top">
   <div class="inner">
      <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison2.jpg" />
   </div>
</div>
<div data-wow-duration="2s" class="foo  foo-2 col-md-3 wow scale-in-ver-top">
   <div class="inner"><img class="" src="https://media.treehugger.com/assets/images/2018/07/nature-benefits.jpg.860x0_q70_crop-scale.jpg" /></div>
</div>
<div data-wow-duration="2s" class="col-md-3 col-md-offset-3 margin-top-20 swing">
   <div class="inner"><img class="wow swing-in-top-fwd" src="https://www.thewaltdisneycompany.com/wp-content/uploads/ENVIRONMENT_header-option_Disney_Conservation_Fund_0348HC.jpg" /></div>
</div>
<div class="col-md-6 col-md-offset-3 bg-color">
   <h1 class="wow fadeInDown">Next Section</h1>
</div>
<!-- HTML -->
<div class="foo foo-text foo-2 col-md-3 col-md-offset-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://www.psychologies.co.uk/sites/default/files/field/image/feelgood%20chemicals.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://kajabi-storefronts-production.global.ssl.fastly.net/kajabi-storefronts-production/blogs/1049/images/BlH7rBrRFGdVF71lofox_TFmaDj07ReWp5C4zcHaw_alex-fergus-look-and-feel-amazing-health-wellness-fat-loss-natural-banner.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-6 col-md-offset-3">
   <div class="inner">
      <h1 class="wow fadeInDown">Hello, world!</h1>
      <p class="wow fadeInUp">Whouaa !!!</p>
   </div>
</div>
<div class="foo foo-3 col-md-6 col-md-offset-3">
   <div class="inner">
      <button type="button" class="btn btn-success">Success</button>
   </div>
</div>
<div class="foo foo-4 col-md-6 col-md-offset-3 wow fadeInDown">
   <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison1.jpg" />
</div>
<div class="foo foo-5 col-md-6 col-md-offset-3">
   <div class="inner">RUBRIQUE 3</div>
</div>
<div data-wow-duration="2s" class="foo foo-1 col-md-3 col-md-offset-3 wow scale-in-ver-top">
   <div class="inner">
      <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison2.jpg" />
   </div>
</div>
<div data-wow-duration="2s" class="foo  foo-2 col-md-3 wow scale-in-ver-top">
   <div class="inner"><img class="" src="https://media.treehugger.com/assets/images/2018/07/nature-benefits.jpg.860x0_q70_crop-scale.jpg" /></div>
</div>
<div data-wow-duration="2s" class="col-md-3 col-md-offset-3 margin-top-20 swing">
   <div class="inner"><img class="wow swing-in-top-fwd" src="https://www.thewaltdisneycompany.com/wp-content/uploads/ENVIRONMENT_header-option_Disney_Conservation_Fund_0348HC.jpg" /></div>
</div>
<div class="col-md-6 col-md-offset-3 bg-color">
   <h1 class="wow fadeInDown">Next Section</h1>
</div>
<!-- HTML -->
<div class="foo foo-text foo-2 col-md-3 col-md-offset-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://www.psychologies.co.uk/sites/default/files/field/image/feelgood%20chemicals.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-3 over-hidden">
   <img class="wow zoominoutsingle" src="https://kajabi-storefronts-production.global.ssl.fastly.net/kajabi-storefronts-production/blogs/1049/images/BlH7rBrRFGdVF71lofox_TFmaDj07ReWp5C4zcHaw_alex-fergus-look-and-feel-amazing-health-wellness-fat-loss-natural-banner.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-6 col-md-offset-3">
   <div class="inner">
      <h1 class="wow fadeInDown">Hello, world!</h1>
      <p class="wow fadeInUp">Whouaa !!!</p>
   </div>
</div>
<div class="foo foo-3 col-md-6 col-md-offset-3">
   <div class="inner">
      <button type="button" class="btn btn-success">Success</button>
   </div>
</div>
<div class="foo foo-4 col-md-6 col-md-offset-3 wow fadeInDown">
   <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison1.jpg" />
</div>
<div class="foo foo-5 col-md-6 col-md-offset-3">
   <div class="inner">RUBRIQUE 3</div>
</div>
<div data-wow-duration="2s" class="foo foo-1 col-md-3 col-md-offset-3 wow scale-in-ver-top">
   <div class="inner">
      <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison2.jpg" />
   </div>
</div>
<div data-wow-duration="2s" class="foo  foo-2 col-md-3 wow scale-in-ver-top">
   <div class="inner"><img class="" src="https://media.treehugger.com/assets/images/2018/07/nature-benefits.jpg.860x0_q70_crop-scale.jpg" /></div>
</div>
<div data-wow-duration="2s" class="col-md-3 col-md-offset-3 margin-top-20 swing">
   <div class="inner"><img class="wow swing-in-top-fwd" src="https://www.thewaltdisneycompany.com/wp-content/uploads/ENVIRONMENT_header-option_Disney_Conservation_Fund_0348HC.jpg" /></div>
</div>
<div class="col-md-6 col-md-offset-3 bg-color">
   <h1 class="wow fadeInDown">Next Section</h1>
</div>
<!-- HTML -->
<div class="foo foo-text foo-2 col-md-3 col-md-offset-3">
   <img class="wow scale-in-ver-top" src="https://www.psychologies.co.uk/sites/default/files/field/image/feelgood%20chemicals.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-3">
   <img class="wow scale-in-ver-top" src="https://kajabi-storefronts-production.global.ssl.fastly.net/kajabi-storefronts-production/blogs/1049/images/BlH7rBrRFGdVF71lofox_TFmaDj07ReWp5C4zcHaw_alex-fergus-look-and-feel-amazing-health-wellness-fat-loss-natural-banner.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-6 col-md-offset-3">
   <div class="inner">
      <h1 class="wow fadeInDown">Hello, world!</h1>
      <p class="wow fadeInUp">Whouaa !!!</p>
   </div>
</div>
<div class="foo foo-3 col-md-6 col-md-offset-3">
   <div class="inner">
      <button type="button" class="btn btn-success">Success</button>
   </div>
</div>
<div class="foo foo-4 col-md-6 col-md-offset-3 wow fadeInDown">
   <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison1.jpg" />
</div>
<div class="foo foo-5 col-md-6 col-md-offset-3">
   <div class="inner">RUBRIQUE 3</div>
</div>
<div data-wow-duration="2s" class="foo foo-1 col-md-3 col-md-offset-3 wow scale-in-ver-top">
   <div class="inner">
      <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison2.jpg" />
   </div>
</div>
<div data-wow-duration="2s" class="foo  foo-2 col-md-3 wow scale-in-ver-top">
   <div class="inner"><img class="" src="https://media.treehugger.com/assets/images/2018/07/nature-benefits.jpg.860x0_q70_crop-scale.jpg" /></div>
</div>
<div data-wow-duration="2s" class="col-md-3 col-md-offset-3 margin-top-20 swing">
   <div class="inner"><img class="wow swing-in-top-fwd" src="https://www.thewaltdisneycompany.com/wp-content/uploads/ENVIRONMENT_header-option_Disney_Conservation_Fund_0348HC.jpg" /></div>
</div>
<div class="col-md-6 col-md-offset-3 bg-color">
   <h1 class="wow fadeInDown">Next Section</h1>
</div>
<!-- HTML -->
<div class="foo foo-text foo-2 col-md-3 col-md-offset-3">
   <img class="wow scale-in-ver-top" src="https://www.psychologies.co.uk/sites/default/files/field/image/feelgood%20chemicals.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-3">
   <img class="wow scale-in-ver-top" src="https://kajabi-storefronts-production.global.ssl.fastly.net/kajabi-storefronts-production/blogs/1049/images/BlH7rBrRFGdVF71lofox_TFmaDj07ReWp5C4zcHaw_alex-fergus-look-and-feel-amazing-health-wellness-fat-loss-natural-banner.jpg" />
</div>
<div class="foo foo-text foo-2 col-md-6 col-md-offset-3">
   <div class="inner">
      <h1 class="wow fadeInDown">Hello, world!</h1>
      <p class="wow fadeInUp">Whouaa !!!</p>
   </div>
</div>
<div class="foo foo-3 col-md-6 col-md-offset-3">
   <div class="inner">
      <button type="button" class="btn btn-success">Success</button>
   </div>
</div>
<div class="foo foo-4 col-md-6 col-md-offset-3 wow fadeInDown">
   <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison1.jpg" />
</div>
<div class="foo foo-5 col-md-6 col-md-offset-3">
   <div class="inner">RUBRIQUE 3</div>
</div>
<div data-wow-duration="2s" class="foo foo-1 col-md-3 col-md-offset-3 wow scale-in-ver-top">
   <div class="inner">
      <img class="" src="http://www.ponpokopon.net/livresillu/unenouvellemaison2.jpg" />
   </div>
</div>
<div data-wow-duration="2s" class="foo  foo-2 col-md-3 wow scale-in-ver-top">
   <div class="inner"><img class="" src="https://media.treehugger.com/assets/images/2018/07/nature-benefits.jpg.860x0_q70_crop-scale.jpg" /></div>
</div>
<div data-wow-duration="2s" class="col-md-3 col-md-offset-3 margin-top-20 swing">
   <div class="inner"><img class="wow swing-in-top-fwd" src="https://www.thewaltdisneycompany.com/wp-content/uploads/ENVIRONMENT_header-option_Disney_Conservation_Fund_0348HC.jpg" /></div>
</div>

body {
    padding-top: 20px;
}


/* set colors*/

 :root {
    --color-1: forestgreen;
    --color-2: lightskyblue;
    --color-3: darksalmon;
    --color-4: palegoldenrod;
    --color-5: mediumvioletred;
}

img {
    width: 100%;
}

.foo {
    margin-bottom: 10px;
    color: white;
}

.navbar {}

.foo .inner {
    padding: 5px;
    min-height: 20vh;
}

.foo-text .inner {
    min-height: 60vh !important;
}


/* apply colors */

.foo-1 .inner {
    background-color: var(--color-1);
}

.foo-2 .inner {
    background-color: var(--color-2);
}

.foo-3 .inner {
    background-color: var(--color-3);
}

.foo-4 .inner {
    background-color: var(--color-4);
}

.foo-5 .inner {
    background-color: var(--color-5);
}

.bg-color {
    background-color: var(--color-5);
    color: #fff;
    margin-top: 20px;
    margin-bottom: 20px;
}

.over-hidden {
    overflow: hidden;
}

.swing {
    overflow: hidden;
}

.scale-in-ver-top {
    -webkit-animation: scale-in-ver-top 0.5s cubic-bezier(0.250, 0.460, 0.450, 0.940) both;
    animation: scale-in-ver-top 0.5s cubic-bezier(0.250, 0.460, 0.450, 0.940) both;
}

@-webkit-keyframes scale-in-ver-top {
    0% {
        -webkit-transform: scaleY(0);
        transform: scaleY(0);
        -webkit-transform-origin: 100% 0%;
        transform-origin: 100% 0%;
        opacity: 1;
    }
    100% {
        -webkit-transform: scaleY(1);
        transform: scaleY(1);
        -webkit-transform-origin: 100% 0%;
        transform-origin: 100% 0%;
        opacity: 1;
    }
}

@keyframes scale-in-ver-top {
    0% {
        -webkit-transform: scaleY(0);
        transform: scaleY(0);
        -webkit-transform-origin: 100% 0%;
        transform-origin: 100% 0%;
        opacity: 1;
    }
    100% {
        -webkit-transform: scaleY(1);
        transform: scaleY(1);
        -webkit-transform-origin: 100% 0%;
        transform-origin: 100% 0%;
        opacity: 1;
    }
}

.swing-in-top-fwd {
    -webkit-animation-name: swing-in-top-fwd;
    animation-name: swing-in-top-fwd;
}

@-webkit-keyframes swing-in-top-fwd {
    0% {
        -webkit-transform: rotateX(-100deg);
        transform: rotateX(-100deg);
        -webkit-transform-origin: top;
        transform-origin: top;
        opacity: 0;
        -webkit-animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
        animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
    }
    100% {
        -webkit-transform: rotateX(0deg);
        transform: rotateX(0deg);
        -webkit-transform-origin: top;
        transform-origin: top;
        opacity: 1;
        -webkit-animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
        animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
    }
}

@keyframes swing-in-top-fwd {
    0% {
        -webkit-transform: rotateX(-100deg);
        transform: rotateX(-100deg);
        -webkit-transform-origin: top;
        transform-origin: top;
        opacity: 0;
        -webkit-animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
        animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
    }
    100% {
        -webkit-transform: rotateX(0deg);
        transform: rotateX(0deg);
        -webkit-transform-origin: top;
        transform-origin: top;
        opacity: 1;
        -webkit-animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
        animation-timing-function: cubic-bezier(0.175, 0.885, 0.320, 1.275);
    }
}

@keyframes zoominoutsinglefeatured {
    0% {
        transform: scale(1, 1);
        webkit-transform: scale(1, 1);
    }
    50% {
        transform: scale(2, 2);
        webkit-transform: scale(2, 2);
    }
    100% {
        transform: scale(1, 1);
        webkit-transform: scale(1, 1);
    }
}

.zoominoutsingle {
    animation-name: zoominoutsinglefeatured;
    webkit-animation-name: zoominoutsinglefeatured;
    -webkit-animation-duration: 10s;
    animation-duration: 10s;
    -webkit-animation-fill-mode: both;
    animation-fill-mode: both;
}

wow = new WOW();
wow.init();

$(".foo-5").hover(function(e) {
    $(this).addClass('animated pulse');
}, function(e) {
    $(this).removeClass('animated pulse');
});
var $animation_elements = $('.wow');
var $window = $(window);

function check_if_in_view() {
    var window_height = $window.height();
    var window_top_position = $window.scrollTop();
    var window_bottom_position = (window_top_position + window_height);

    $.each($animation_elements, function() {
        var $element = $(this);
        var element_height = $element.outerHeight();
        var element_top_position = $element.offset().top;
        var element_bottom_position = (element_top_position + element_height);

        //check to see if this current container is within viewport
        if ((element_bottom_position >= window_top_position) &&
            (element_top_position <= window_bottom_position)) {
            $element.removeClass('animated');
            $element.addClass('animated');
        } else {
            $element.css({
                'visibility': 'hidden',
                'animation-name': 'none'
            }).removeClass('animated');
            wow.addBox(this);
        }
    });
}
WOW.prototype.addBox = function(element) {
    this.boxes.push(element);
};
$window.on('scroll resize', check_if_in_view);

update:- This is just an example that i am using in webpage. Web page has different number of sections apporx. 20 sections and all are having 10 or more images. So when we are running that much images with animations the performance goes down.

I have checked it on mac Safari 11 & 12, the animation and scroll is not smooth. There is jerkiness while scrolling and animations are very slow with jerks.

Answer 1

You can probably gain a lot of performance by using Intersection Observer (IO) instead of listening to the scroll event. IO was introduced because listening to the scroll event and calculating height/width of elements results in poor performance.

First you have to create a new observer:

var options = {
  rootMargin: '0px',
  threshold: 1.0
 }

var observer = new IntersectionObserver(callback, options);

Here we specify that once the observed element is 100% visible, some callback should be executed.

Then you have to specify which items to observe, in your case I think this would be:

var target = document.querySelector('.wow');
observer.observe(target);

So we define that once any element with the class "wow" is visible on the page, the callback is getting executed:

var callback = function(entries, observer) { 
  entries.forEach(entry => {
  // Each entry describes an intersection change for one observed
  // target element:
  });
};

Here you specify what should happen for each "wow"-Element in your page that is getting visible.

If you are using CSS for your animations and not JS then the animations should now be smooth. It also depends on what parameters you are animating, here is a good list of properties to avoid animating with CSS.

I won't copy the whole list here, but the most important ones would be padding, width, height and position.

Edit: If you need to support older browsers than use this (official) polyfill from w3c, it recreates intersection observer with listening to scroll events. So it will still be slower on older browsers, nothing you can do about it here. But on newer ones there will be an increase in performance.

Answer 2

You can use lazy loading for animations and perform in a better way the loading of view elements. JQuery Lazy

Answer 3

Since it looks like you're only using animated pulse, and are already adding and removing the animated class, I'd highly suggest using CSS animations.

CSS animations are rendered with the GPU and do not use the main thread like JavaScript does. They're super smooth and performant!

Check out this Codepen I found on Google creating a pulsing animated icon: https://codepen.io/igorsheg/pen/MBpwGw