How to Trigger multiple css animations on scroll

Question

I'm using several CSS animations on a design. My problem is these animations get triggered only once, when the page first loads. I need them to be triggered every time the user scrolls by them, whether going up or down the page, and nothing seems to be responding to my Javascript. I have a colored box that slides in left, and body copy + header that will fade in from the bottom. I want these two separate animations to be slightly offset in duration, with the text coming in after the box has slid in about half way. I tried nesting these divs into one so that they all are revealed at the same point on scroll, and I've also tried treating them as separate entities within JavaScript.

$(window).scroll(function() {
  $('#Featuring_Animated').each(function() {
    var imagePos = $(this).offset().top;
    var imageHeight = $(this).height();
    var topOfWindow = $(window).scrollTop();

    if (imagePos < topOfWindow + imageHeight && imagePos + imageHeight > topOfWindow) {
      $(this).addClass("slide-in-left");
    } else {
      $(this).removeClass("slide-in-left");
    }
  });
});

$('.element-to-hide').css('visibility', 'hidden');

/**
 * ----------------------------------------
 * animation slide-in-left
 * ----------------------------------------
 */

.Featuring_Textbox {
  -webkit-animation: slide-in-left .5s cubic-bezier(0.250, 0.460, 0.450, 0.940) both;
  animation: slide-in-left .5s cubic-bezier(0.250, 0.460, 0.450, 0.940) both;
  visibility: visible !important;
}

@-webkit-keyframes slide-in-left {
  0% {
    -webkit-transform: translateX(-1000px);
    transform: translateX(-1000px);
    opacity: 0;
  }
  100% {
    -webkit-transform: translateX(0);
    transform: translateX(0);
    opacity: 1;
  }
}


/**
 * ----------------------------------------
 * animation fade-in-bottom left sections
 * ----------------------------------------
 */

#Featuring_About,
#Featuring_Heading {
  -webkit-animation: fade-in-bottom 0.6s cubic-bezier(0.390, 0.575, 0.565, 1.000) .3s both;
  animation: fade-in-bottom 0.6s cubic-bezier(0.390, 0.575, 0.565, 1.000) .3s both;
  visibility: visible !important;
}

@-webkit-keyframes fade-in-bottom {
  0% {
    -webkit-transform: translateY(50px);
    transform: translateY(50px);
    opacity: 0;
  }
  100% {
    -webkit-transform: translateY(0);
    transform: translateY(0);
    opacity: 1;
  }
}


/**
 * ----------------------------------------
 * animation fade-in-bottom left sections
 * ----------------------------------------
 */

#Featuring_Textbox {
  opacity: 0.9;
  fill: #3B4A5C;
}

.Featuring_Textbox {
  position: absolute;
  overflow: visible;
  width: 640px;
  height: 552px;
  left: 0px;
  top: 0px;
}

#Featuring_About {
  left: 74px;
  top: 238px;
  position: absolute;
  text-align: left;
  font-size: 18px;
  color: white;
}

#Featuring_Heading {
  left: 74px;
  top: 143px;
  position: absolute;
  text-align: left;
  font-size: 40px;
  color: white;
}

<html>
<head>
<script language="JavaScript" type="text/javascript" src="colocation.js"></script>
</head>

<div class="Featuring_Animated element-to-hide" style="visibility:visible;">
  <svg class="Featuring_Textbox">
            <rect id="Featuring_Textbox" rx="0" ry="0" x="0" y="0" width="640" height="552"></rect>
         </svg>
  <div id="Featuring_About">
    <span>Sample Text</span>
  </div>
  <div id="Featuring_Heading">
    <span>FEATURING</span>
  </div>
</div>

</html>

Phlex · Accepted Answer · 2020-08-26 01:05:39Z

If you dont want a library you can do this. (cobbled together from other contributors,ty) You can add different effects to different selectors. Animation triggers once when set percentage of element is visible (isInViewport - 2nd parameter, currently set to 35%). Triggered only once.

//every element needs to have a "hidden" class, ie. "visability:hidden" if starting state is hidden (fad-in effects and similar)

var elemList = {elements:[ //add elements and animations here
    {elem:"#home-description", animation:"element-animation"},
    {elem:".nav-item",animation:"slide-in-top"}
]};

var isInViewport = function(el, percentVisible) {
    let
    rect = el.getBoundingClientRect(),
        windowHeight = (window.innerHeight || document.documentElement.clientHeight);

    return !(
        Math.floor(100 - (((rect.top >= 0 ? 0 : rect.top) / +-(rect.height / 1)) * 100)) < percentVisible ||
        Math.floor(100 - ((rect.bottom - windowHeight) / rect.height) * 100) < percentVisible
    )
};



function check(){
    var eArray = elemList.elements;

    if (eArray.length >= 1){  
        eArray.forEach( function(e,i){

            if (e.elem){ //check if empty
                let el = document.querySelectorAll(e.elem);

                if (el.length >= 1){

                    el.forEach( function(x,y){
                        if (isInViewport(x,35)){
                            x.classList.remove("hidden") //remove this if element should be visible
                            x.classList.add(e.animation)
                            eArray.splice(i, 1)

                        }
                    })
                }
            }
        })
    }
}


window.addEventListener('load', function () {
    check();
    document.addEventListener('scroll', function () {
        check();
    })
}, {
    passive: true
});

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