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How to “Lazy Load” Embedded YouTube Videos

Embedding a Youtube video has become a completely normal process for anyone involved with the web; copy, paste, done. However, pulling in an external resource like a Youtube video may slow down a web page’s load performance, especially if there are two or more videos embedded on the same page.

By embedding videos we request more than just a video file. A number of resources are fetched, including JavaScript files, a stylesheet, images, and advertisements. And as you can from the screenshot below, two Youtube videos equates to 22 HTTP requests with a total of 624kb downloaded. These numbers will climb as we embed more videos on the page.

HTML Structure

<div class="wrapper">
  <div class="youtube" data-embed="AqcjdkPMPJA">
    <div class="play-button"></div>
  </div>
</div>

CSS

html {
  background-color: #f3f3f3;
}
.wrapper {
  max-width: 680px;
  margin: 60px auto;
  padding: 0 20px;
}

.youtube {
  background-color: #000;
  margin-bottom: 30px;
  position: relative;
  padding-top: 56.25%;
  overflow: hidden;
  cursor: pointer;
}
.youtube img {
  width: 100%;
  top: -16.82%;
  left: 0;
  opacity: 0.7;
}
.youtube .play-button {
  width: 90px;
  height: 60px;
  background-color: #333;
  box-shadow: 0 0 30px rgba( 0,0,0,0.6 );
  z-index: 1;
  opacity: 0.8;
  border-radius: 6px;
}
.youtube .play-button:before {
  content: "";
  border-style: solid;
  border-width: 15px 0 15px 26.0px;
  border-color: transparent transparent transparent #fff;
}
.youtube img,
.youtube .play-button {
  cursor: pointer;
}
.youtube img,
.youtube iframe,
.youtube .play-button,
.youtube .play-button:before {
  position: absolute;
}
.youtube .play-button,
.youtube .play-button:before {
  top: 50%;
  left: 50%;
  transform: translate3d( -50%, -50%, 0 );
}
.youtube iframe {
  height: 100%;
  width: 100%;
  top: 0;
  left: 0;
}

Javascript

( function() {

  var youtube = document.querySelectorAll( ".youtube" );
  
  for (var i = 0; i < youtube.length; i++) {
    
    var source = "https://img.youtube.com/vi/"+ youtube[i].dataset.embed +"/sddefault.jpg";
    
    var image = new Image();
        image.src = source;
        image.addEventListener( "load", function() {
          youtube[ i ].appendChild( image );
        }( i ) );
    
        youtube[i].addEventListener( "click", function() {

          var iframe = document.createElement( "iframe" );

              iframe.setAttribute( "frameborder", "0" );
              iframe.setAttribute( "allowfullscreen", "" );
              iframe.setAttribute( "src", "https://www.youtube.com/embed/"+ this.dataset.embed +"?rel=0&showinfo=0&autoplay=1" );

              this.innerHTML = "";
              this.appendChild( iframe );
        } );  
  };
  
} )();

Website

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