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HTML

              
                <div class="ale" data-ale-type="diagonal" data-ale-src="https://crossorigin.me/https://zachsaucier.com/images/grapes.jpg"></div>

<div class="centered">
  <h2>Asset loading effects</h2>
  <p>For more loading effects, source code, and an article of how it works, check out <a href="https://github.com/ZachSaucier/Asset-Loading-Effects/tree/master">the GitHub page</a>.
</div>
              
            
!

CSS

              
                $transDur: 0.5s;

.ale {
  /* This sizes each asset element so that the width is 1.5 times bigger than the height. 
     If changed, the positioning some sub elements will need to be changed as 
     well. */
  height:0;
  padding-bottom:66%;
  
  /* This part is for the effect itself */
  background-size:cover;
  position:relative;
  overflow:hidden;

  /* Add a default fade in for every effect */
  &::after {
    z-index:0;
    content:'';
    position:absolute;
    top:0;
    width:100%;
    height:100%;
    background-color:inherit;
  }
  &.complete::after {
      opacity:0;
      transition:$transDur * 2;
  }
        
  /* Make sure any SVG or ::before elements are above ::after elements */
  > svg,
  &::before {
    z-index:1;
  }
  
  /* The diagonal loader */
  &[data-ale-type="diagonal"] {
    color:white;
    
    /* Position the SVG loader diagonally */
    > svg {
      position:absolute;
      top:50%;
      width:125%;
      -webkit-transform:translate(-10%, -50%) rotate(-33.333deg);
      transform:translate(-10%, -50%) rotate(-33.333deg);
    }
    /* Create each half to be separated in the animation */
    &::after,
    &::before {
      content:"";
      width:125%;
      height:100%;
      position:absolute;
      background:currentColor;
    }
    /* Position the left side */
    &::before {
      -webkit-transform-origin:bottom left;
      transform-origin:bottom left;
      -webkit-transform:rotate(-33.333deg);
      transform:rotate(-33.333deg);
    }
    /* Position the right side */
    &::after {
      right:0;
      -webkit-transform-origin:top right;
      transform-origin:top right;
      -webkit-transform:rotate(-33.333deg);
      transform:rotate(-33.333deg);
    }
    
    /* Set the complete state for each part */
    &.complete {
      /* Fade out the SVG */
      > svg { 
        transition:$transDur / 2; 
        opacity:0;
      }
      
      /* Slide out both sides */
      &::before {
        transition:$transDur * 2;
        -webkit-transform:rotate(-33.333deg) translateY(-100%);
        transform:rotate(-33.333deg) translateY(-100%);
      }
      &::after {
        opacity:1;
        transition:$transDur * 2;
        -webkit-transform:rotate(-33.333deg) translateY(100%);
        transform:rotate(-33.333deg) translateY(100%);
      }
    }
  }
}



@import url(https://fonts.googleapis.com/css?family=Open+Sans);

body {
	font-size:18px;
	font-family: 'Open Sans', sans-serif;
}
.centered {
  margin:0 auto;
  max-width:900px;
  box-sizing:border-box;
  padding:20px;
}
              
            
!

JS

              
                // The elements that are the to be used for the asset
var assetElems = document.querySelectorAll(".ale"), 
    urlCreator = window.URL || window.webkitURL; // For URL creator usage later
    
// Add the asset loading effect for each element
[].forEach.call(assetElems, loadAsset); 

// Load the asset in the way specified by the data attribute
function loadAsset(elem) {
    // Determine which loader to create
    var progressBarElem = getProgressBarElem(),
        isVid = elem.getAttribute("data-ale-isVid") != undefined ? elem.getAttribute("data-ale-isVid") : false,
        assetLoc = elem.getAttribute("data-ale-src");

    // Load the asset via XHR so that we can track the progress    
    var req = new XMLHttpRequest();
    // Attach the finished load listener
    req.onload = loadFinished;
    // Attach the progress listener
    req.onprogress = loading; 
    // Actually make the request
    req.open('GET', assetLoc, true);
    req.responseType = 'blob'; // This must be after the open - FF can't handle do it before https://bugzilla.mozilla.org/show_bug.cgi?id=1110761
    req.send();

    // Determine which progress bar to use given the data attribute and return it
    function getProgressBarElem() {
        var type = elem.getAttribute("data-ale-type");
        
        // Choose the progress bar type based on the lil-type
        if(type !== "diagonal") {
            console.log("A diagonal type was not given! Creating one anyway");
        } else { 
            var line = new ProgressBar.Line(elem);
            
            // Fix an IE issue
            line.svg.setAttribute("preserveAspectRatio", "xMinYMid");
            
            return line;
        } 
    }

    // Update the progress bar with the current value
    function loading(evt) {
        if (evt.lengthComputable) {
            // ProgressBar.js animates using 0.0-1.0 as a range, so we need the progress in terms of that
            progressBarElem.animate(evt.loaded / evt.total);
        }
    }

    // Remove the loader when it's done and show the image
    function loadFinished() {
        // Currently, if it's not a video it's an image
        if(!isVid) {
            // Create a URL for the given response
            var imgUrl = urlCreator.createObjectURL(req.response);
            // Set that URL as the background of the element given
            elem.style.backgroundImage = 'url(' + imgUrl + ')';
        } else {
            var video = document.createElement('video');
            video.controls = true;
            video.src = urlCreator.createObjectURL(req.response);
            elem.appendChild(video); // Append the video since we can't do a background-video
        }
        
        // Finish the animation
        progressBarElem.animate(1, function () {            
            // Add the "complete" class to show it's done 
            elem.classList.add("complete");
        });
    }
}
              
            
!
999px

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