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Here you can Sed posuere consectetur est at lobortis. Donec ullamcorper nulla non metus auctor fringilla. Maecenas sed diam eget risus varius blandit sit amet non magna. Donec id elit non mi porta gravida at eget metus. Praesent commodo cursus magna, vel scelerisque nisl consectetur et.

HTML

              
                <h1>How to lazy load images in a performant way</h1>
<p>
There is also an example image how to use it with an background image.
  <br>
  Take a look at the <a href="https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API#Browser_compatibility">Browser support table.</a>
  and use <a href="https://www.npmjs.com/package/intersection-observer#browser-support">Polyfill</a> for better support. This one here does work properly in Safari, thanks to the <a href="https://polyfill.io/v2/polyfill.min.js?features=IntersectionObserver">Polyfill Script</a> I added to the source. You will see that the HTML is bloated up quite a bit, this is because I added some noscript fallbacks for no-js browsing people.</p>

<noscript>
  <!-- 
    Hide the lazy load images if we do not have JS
  -->
  <style>
    .image__list-lazy-image { 
      display: none;
    }
  </style>
</noscript>
<div class="image-container">
  <ul class="image__list">
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg" alt="blue lake with surrounding mountains">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg" alt="blue lake with surrounding mountains">
    </li>
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796305/pexels-photo-104336.jpg" alt="street in the middle of a forrest">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796305/pexels-photo-104336.jpg" alt="street in the middle of a forrest">
    </li>
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796376/les-anderson-175603.jpg" alt="two elder people opening togehter a christmas present">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796376/les-anderson-175603.jpg" alt="two elder people opening togehter a christmas present">
    </li>
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796381/pexels-photo-737108.jpg" alt="black and white clothes hanging on a clothes rail">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796381/pexels-photo-737108.jpg" alt="black and white clothes hanging on a clothes rail">
    </li>
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796475/tobias-van-schneider-122288.jpg" alt="book collection photographed from top">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796475/tobias-van-schneider-122288.jpg" alt="book collection photographed from top">
    </li>
    <li class="image__list-item">
      <noscript>
        <img class="image__list-image" src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg" alt="two elder people opening togehter a christmas present">
      </noscript>
      <img class="image__list-image image__list-lazy-image" data-src="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg" alt="brown meadow with a tower in the very back">
    </li>
    <li class="image__list-item">
      <noscript>
        <div class="image__list-image--bg" style="background-image:url('http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg');" alt="two elder people opening togehter a christmas present"></div>
      </noscript>
      <div class="image__list-image--bg image__list-lazy-image" data-lazybackground="http://res.cloudinary.com/dsteinel/image/upload/c_scale,w_450/v1523796300/pexels-photo-559768.jpg">
      </div>
    </li>
  </ul>
</div>
              
            
!

CSS

              
                body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  max-width: 450px;
  margin: 0 auto;
  padding: 2em 0;
  font-size: 18px;
  line-height: 1.5;
}

h1 {
  display: block;
  margin: 0 auto 2rem;
  line-height: 1.1;
}

ul {
  padding: 0;
  margin: 0;
  list-style-type: none;
}

a {
  color: #A55; /* HAHA! */
}

p {
  margin-bottom: 3rem;
}

.image__list-image {
  opacity: 1;
  min-height: 100%;
}

.image__list-lazy-image { 
  opacity: 0;
}

.image__list-item {
  width: 100%;
  height: 250px;
  overflow: hidden;
  margin-bottom: 40px;
}

.image__list-image--bg {
  background-size: cover;
  background-repeat: no-repeat;
  height: 100%;
}
              
            
!

JS

              
                const options = {
  rootMargin: '0px',
  threshold: 0.1
}
const allTheLazyImages = document.querySelectorAll('.image__list-lazy-image');
let observer;

// Does your browser support InersectionObserver?
if('IntersectionObserver' in window) {
  observer = new IntersectionObserver(lazyLoader, options);

  // select all our image which we want to have lazy loaded
  allTheLazyImages.forEach(image => {
    // put them in the observer
    observer.observe(image);
  });
} else {
  allTheLazyImages.forEach(image => {
    lazyLoadImage(image); // if it is not supported, load all
  });
}

function lazyLoader (entries) {
  // loop through all images
  entries.forEach(entry => {
    // does the viewport hit the current image
    if (entry.intersectionRatio > 0) {
      // yes! load the image
      lazyLoadImage(entry.target);
    }
  });
}

function lazyLoadImage(observedImage) { 
  /**
    *  We hit an observed image!
    *  First, remove the lazy loading class. This will show the image
    *  Then remove the observer
    */
  observedImage.classList.remove('image__list-lazy-image');
  
  // If we have an background image, replace the source with the data-lazyBackground attribute
  if(observedImage.dataset.lazybackground) {
    observedImage.style.backgroundImage = `url(${observedImage.dataset.lazybackground})`;
  }
  
  // does it have a data attribute with image-src?
  if (observedImage.getAttribute('data-src')) {
    // yes! So lets make the image source equal to the data image source and render it!
    observedImage.src = observedImage.dataset.src;
  
    if('IntersectionObserver' in window) {
      // now that the image has bee renderes, we don't need to observe it anymore
      observer.unobserve(observedImage);
    }
  }      
}
              
            
!
999px

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