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HTML 

              
                <header class=lateload-container>

  <div class="lateload-img lateload-img-1" data-lateload-src="https://websemantics.uk/articles/late-loaded-blurred-image-replacement/demo/digital-tunnel.jpg">
    <div></div>
  </div>

  <div class=lateload-copy>

    <h1><a target=_blank href="http://websemantics.uk/articles/late-loaded-blurred-image-replacement/">Blurred image late-load replacement</a></h1>
    <p><span>See full <a target=_blank href="http://websemantics.uk/articles/late-loaded-blurred-image-replacement/">article</a> for more details.</span></p>
    <p><span>Vanilla JavaScript, with CSS fallback.</span></p>
    <p style="font-size:larger"><span>A 3 second delay is applied to simulate poor network connectivity</span></p>

  </div>

</header>

<main>
  
  <h2><span>Improve perceived page-load times</span></h2>
  
  <p>Display  blurry, low resolution, image(s) immediately, without any extra HTTP requests.</p> 
<p>Once page has fully loaded, fetch the high resolution image(s), then cross-fade onto display.</p>
  
  <p style="color:#ff0">As used on the <a style="color:#ff0" href="https://websemantics.uk/portfolio/2016/finest-wine-bar/" target=_blank title="[new window]">Tesco finest wine bar</a> page.</p>

<p><a target=_blank href="http://websemantics.uk/articles/late-loaded-blurred-image-replacement/">Late-loaded blurred image replacement &ndash; article</a></p>
  
  <p>Digital Tunnel image from <a target=_blank href="http://www.linkedinbackground.com/abstract/digital-tunnel/">Linked In Backgrounds</a></p>

</main>

[[[https://codepen.io/2kool2/pen/mKeeGM]]]
!

CSS 

              
                /* General styles */

body {
  margin: 0;
  color: #fff;
  background: #000;
  font-family: sans-serif;
  line-height: 1.5;
  text-align: center;
  text-shadow: 0 2px 4px #000;
  background-image: url("data:image/svg+xml;utf8,<svg style='opacity:.75' width='1200' height='256' viewBox='0 0 1200 256' xmlns='http://www.w3.org/2000/svg'><defs><filter id='noise'><feTurbulence type='fractalNoise' baseFrequency='.4'></feTurbulence></filter></defs><rect height='256' width='1200' filter='url(%23noise)' opacity='0.3'/></svg>");
}

h1 a,
h2 span,
p span {
  font-weight: 100;
  padding: .5rem 1rem;
  background-color: rgba(0, 0, 0, 0.25);
  text-decoration: none;
}

a {color: #fff;}



/* Blurred background-image lazy-load */


/* Container defines the size */

.lateload-container {
  position: relative;
  overflow: hidden;
  min-height: 400px;

  display: flex;
  align-items: center;
  justify-content: center;
}


/* The three image layers: */

.lateload-img,  /* bottom layer */
.lateload-img div,  /* middle layer */
.lateload-img div::before {  /* top layer */
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-position: center;
  background-size: cover;
  z-index: -1;
}


/* 2 KB images are applied to both top & middle layers */

.lateload-img-1 div::before,
.lateload-img-1 div {
  /* digital-tunnel.small.jpg - Less than 2kb strongly suggested */
  background-image: url(data:image/jpeg;base64,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);
}


/* Top-most layer has the blur applied */

.lateload-img div::before {
  content: "";
  filter: blur(10px);
}


/*
  Middle layer: No blur, required to keep the container edges sharp.

  Bottom layer: .hero-bg has background-image added via script (when available).
                Upon image load, script fades out the top two layers.
*/


/* When no scripting is available use CSS instead. */


/* No JS: Add image to bottom layer */

.noJS .lateload-img {
  background-image: url(http://websemantics.uk/articles/late-loaded-blurred-image-replacement/demo/digital-tunnel.jpg);
}


/* No JS: Fade out blur layers */

.noJS .lateload-img div {
  animation: fadeOut 1s ease-out 3s forwards;
}

@keyframes fadeOut {
  to {
    opacity: 0
  }
}
!

JS 

              
                // Uncomment the next line to test the no-script variant
// document.documentElement.classList.add("noJS");

var LateLoadDataSrcImages = (function() {

  // Browser support required for:
  //    addEventListener,
  //    requestAnimationFrame,
  //    getElementsByClassName

  "use strict";

  var lateloadClass = "lateload-img",
      lateloadDataAttr = "data-lateload-src";

  var _fadeOut = function(el) {

    el.style.opacity = 1;

    (function _fade() {

      if ((el.style.opacity -= 0.05) < 0) {

        // tidy up and remove from DOM
        el.parentNode.removeChild(el);
      } else {
        window.requestAnimationFrame(_fade);
      }

    })();

  };

  var _displayImage = function(img) {

    var obj = img.divObj;

    window.requestAnimationFrame(function() {

      var childDivs = obj.getElementsByTagName("div");

      // Add image to the bottom layer
      // It's unseen, behind the top & middle layer, hopefully no paint or reflow occurs (check it!).
      obj.style.backgroundImage = "url(" + img.src + ")";

      // fade out the middle layer, it'll take the top layer with it.
      if (childDivs) {

        // small delay to emulate a poor connection - Remove in production
        setTimeout(function(){
          _fadeOut(childDivs[0]);
        }, 1500);

      }

    });
  };

  var _requestImage = function (obj, src) {

    var img = new Image();

    img.divObj = obj;
    img.addEventListener("load", function() {
      _displayImage(img);
    }, false);
    img.src = src;

  };

  var _initialise = function () {

    // tidy up
    window.removeEventListener("load", _initialise);
    
    var lateLoads = document.getElementsByClassName(lateloadClass);
    var len = lateLoads.length;
    var dataAttr
    if (len) {
      for (var i = 0; i < len; i++) {
        dataAttr = lateLoads[i].getAttribute(lateloadDataAttr);
        if (dataAttr) {
          _requestImage(lateLoads[i], dataAttr);
        }
      }
    }
    
/* Replaced with the rubbish for-loop (above) for Chrome, cotton socks, bless:
    let lateLoads = document.getElementsByClassName(lateloadClass);
    for (let lateLoadObj of lateLoads) {
      let dataAttr = lateLoadObj.getAttribute(lateloadDataAttr);
      if (dataAttr) {
        _requestImage(lateLoadObj, dataAttr);
      }
    }
*/
    
  };

  // test required features are supported here before initialising
  var featuresSupported = true;
  if (featuresSupported) {
    window.addEventListener("load", _initialise, false);
  }
  

}());
!
999px

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