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HTML

              
                <html ng-app="Demo" ng-controller="AppController">
  <head>
    <meta charset="utf-8" />
    <title>
      Lazy Loading Images With AngularJS
    </title>
  </head>
  <body>
    <h1>
      Lazy Loading Images With AngularJS
    </h1>
   
    <p>
      You have {{ photos.size }} photos in your set.
   
      <a ng-click="rebuildSet()">Rebuild set</a>.
      <a ng-click="changeSource()">Change src</a>.
      <a ng-click="clearPhotos()">Clear</a>.
    </p>
   
    <a ng-show="isBoxVisible" ng-click="hideBox()" class="box">
      This is a big thing that may change,
      causing the DOCUMENT HEIGHT to change.
    </a>
   
    <ul class="photos">
   
      <li ng-repeat="photo in photos" class="photo">
   
        <img
          bn-lazy-src="{{ photo.src }}"
          width="150"
          height="150"
          alt="Christina Cox"
          />
      </li>
    </ul>
  </body>
</html>
              
            
!

CSS

              
                /* Add "click" styles because newer releases of AngularJS don't seem to add the HREF value. */
		a[ ng-click ] {
			cursor: pointer ;
			text-decoration: underline ;
		}
 
		a.box {
			background-color: #FAFAFA ;
			border: 1px solid #CCCCCC ;
			display: block ;
			height: 200px ;
			line-height: 200px ;
			text-align: center ;
			width: 684px ;
		}
 
		ul.photos {
			list-style-type: none ;
			margin: 16px 0px 16px 0px ;
			padding: 0px 0px 0px 0px ;
			width: 700px ;
		}
 
		ul.photos:after {
			content: "" ;
			clear: both ;
			display: block ;
			height: 0px ;
		}
 
		li.photo {
			background-color: #FAFAFA ;
			border: 1px solid #CCCCCC ;
			border-radius: 4px 4px 4px 4px ;
			float: left ;
			margin: 0px 10px 10px 0px ;
			padding: 5px 5px 5px 5px ;
		}
 
		li.photo img {
			border: 1px solid #EEEEEE ;
			border-radius: 3px 3px 3px 3px ;
			display: block ;
		}
 
		img[ bn-lazy-src ] {
			background-image: url( "https://bennadel.github.io/JavaScript-Demos/demos/lazy-src-angularjs/checkered.png");
		}
              
            
!

JS

              
                // Create an application module for our demo.
		var app = angular.module( "Demo", [] );
		// -------------------------------------------------- //
		// -------------------------------------------------- //
 
		// I control the root of the application.
		app.controller(
			"AppController",
			function( $scope ) {
 
				// I flag the visibility of the big box.
				$scope.isBoxVisible = true;
 
				// Build up a large set of images, all with unique
				// SRC values so that the browser cannot cache them.
				$scope.photos = buildPhotoSet( 1000 );
 
 
				// ---
				// PUBLIC METHODS.
				// ---
 
 
				// I change the SRC values of the existing photo set
				// in order to examine how changes to source will
				// affect rendered / non-rendered images.
				$scope.changeSource = function() {
 
					var now = ( new Date() ).getTime();
 
					// Update all SRC attribute to point to "1.jpg".
					for ( var i = 0 ; i < $scope.photos.length ; i++ ) {
 
						var photo = $scope.photos[ i ];
 
						photo.src = photo.src.replace( /\d\./i, "1." );
 
					}
 
				};
 
 
				// I clear the current photo set.
				$scope.clearPhotos = function() {
 
					$scope.photos = [];
 
				};
 
 
				// I hide the big box, allowing the document to change
				// its dimensions (and possibly show more images than
				// were visible beforehand).
				$scope.hideBox = function() {
 
					$scope.isBoxVisible = false;
 
				};
 
 
				// I rebuild the entire photo set.
				$scope.rebuildSet = function() {
 
					$scope.photos = buildPhotoSet( 20 );
 
				};
 
 
				// ---
				// PRIVATE METHODS.
				// ---
 
 
				// I return a photo set of the given size. Each photo
				// will have a unique SRC value.
				function buildPhotoSet( size ) {
 
					var photos = [];
					var now = ( new Date() ).getTime();
 
					for ( var i = 0 ; i < size ; i++ ) {
 
						var index = ( ( i % 3 ) + 1 );
						var version = ( now + i );
 
						photos.push({
							id: ( i + 1 ),
							src: ( "https://bennadel.github.io/JavaScript-Demos/demos/lazy-src-angularjs/christina-cox-" + index + ".jpg?v=" + version )
						});
 
					}
 
					return( photos );
 
				}
 
			}
		);
 
 
		// -------------------------------------------------- //
		// -------------------------------------------------- //
 
 
		// I lazily load the images, when they come into view.
		app.directive(
			"bnLazySrc",
			function( $window, $document ) {
 
 
				// I manage all the images that are currently being
				// monitored on the page for lazy loading.
				var lazyLoader = (function() {
 
					// I maintain a list of images that lazy-loading
					// and have yet to be rendered.
					var images = [];
 
					// I define the render timer for the lazy loading
					// images to that the DOM-querying (for offsets)
					// is chunked in groups.
					var renderTimer = null;
					var renderDelay = 100;
 
					// I cache the window element as a jQuery reference.
					var win = $( $window );
 
					// I cache the document document height so that
					// we can respond to changes in the height due to
					// dynamic content.
					var doc = $document;
					var documentHeight = doc.height();
					var documentTimer = null;
					var documentDelay = 2000;
 
					// I determine if the window dimension events
					// (ie. resize, scroll) are currenlty being
					// monitored for changes.
					var isWatchingWindow = false;
 
 
					// ---
					// PUBLIC METHODS.
					// ---
 
 
					// I start monitoring the given image for visibility
					// and then render it when necessary.
					function addImage( image ) {
 
						images.push( image );
 
						if ( ! renderTimer ) {
 
							startRenderTimer();
 
						}
 
						if ( ! isWatchingWindow ) {
 
							startWatchingWindow();
 
						}
 
					}
 
 
					// I remove the given image from the render queue.
					function removeImage( image ) {
 
						// Remove the given image from the render queue.
						for ( var i = 0 ; i < images.length ; i++ ) {
 
							if ( images[ i ] === image ) {
 
								images.splice( i, 1 );
								break;
 
							}
 
						}
 
						// If removing the given image has cleared the
						// render queue, then we can stop monitoring
						// the window and the image queue.
						if ( ! images.length ) {
 
							clearRenderTimer();
 
							stopWatchingWindow();
 
						}
 
					}
 
 
					// ---
					// PRIVATE METHODS.
					// ---
 
 
					// I check the document height to see if it's changed.
					function checkDocumentHeight() {
 
						// If the render time is currently active, then
						// don't bother getting the document height -
						// it won't actually do anything.
						if ( renderTimer ) {
 
							return;
 
						}
 
						var currentDocumentHeight = doc.height();
 
						// If the height has not changed, then ignore -
						// no more images could have come into view.
						if ( currentDocumentHeight === documentHeight ) {
 
							return;
 
						}
 
						// Cache the new document height.
						documentHeight = currentDocumentHeight;
 
						startRenderTimer();
 
					}
 
 
					// I check the lazy-load images that have yet to
					// be rendered.
					function checkImages() {
 
						// Log here so we can see how often this
						// gets called during page activity.
						console.log( "Checking for visible images..." );
 
						var visible = [];
						var hidden = [];
 
						// Determine the window dimensions.
						var windowHeight = win.height();
						var scrollTop = win.scrollTop();
 
						// Calculate the viewport offsets.
						var topFoldOffset = scrollTop;
						var bottomFoldOffset = ( topFoldOffset + windowHeight );
 
						// Query the DOM for layout and seperate the
						// images into two different categories: those
						// that are now in the viewport and those that
						// still remain hidden.
						for ( var i = 0 ; i < images.length ; i++ ) {
 
							var image = images[ i ];
 
							if ( image.isVisible( topFoldOffset, bottomFoldOffset ) ) {
 
								visible.push( image );
 
							} else {
 
								hidden.push( image );
 
							}
 
						}
 
						// Update the DOM with new image source values.
						for ( var i = 0 ; i < visible.length ; i++ ) {
 
							visible[ i ].render();
 
						}
 
						// Keep the still-hidden images as the new
						// image queue to be monitored.
						images = hidden;
 
						// Clear the render timer so that it can be set
						// again in response to window changes.
						clearRenderTimer();
 
						// If we've rendered all the images, then stop
						// monitoring the window for changes.
						if ( ! images.length ) {
 
							stopWatchingWindow();
 
						}
 
					}
 
 
					// I clear the render timer so that we can easily
					// check to see if the timer is running.
					function clearRenderTimer() {
 
						clearTimeout( renderTimer );
 
						renderTimer = null;
 
					}
 
 
					// I start the render time, allowing more images to
					// be added to the images queue before the render
					// action is executed.
					function startRenderTimer() {
 
						renderTimer = setTimeout( checkImages, renderDelay );
 
					}
 
 
					// I start watching the window for changes in dimension.
					function startWatchingWindow() {
 
						isWatchingWindow = true;
 
						// Listen for window changes.
						win.on( "resize.bnLazySrc", windowChanged );
						win.on( "scroll.bnLazySrc", windowChanged );
 
						// Set up a timer to watch for document-height changes.
						documentTimer = setInterval( checkDocumentHeight, documentDelay );
 
					}
 
 
					// I stop watching the window for changes in dimension.
					function stopWatchingWindow() {
 
						isWatchingWindow = false;
 
						// Stop watching for window changes.
						win.off( "resize.bnLazySrc" );
						win.off( "scroll.bnLazySrc" );
 
						// Stop watching for document changes.
						clearInterval( documentTimer );
 
					}
 
 
					// I start the render time if the window changes.
					function windowChanged() {
 
						if ( ! renderTimer ) {
 
							startRenderTimer();
 
						}
 
					}
 
 
					// Return the public API.
					return({
						addImage: addImage,
						removeImage: removeImage
					});
 
				})();
 
 
				// ------------------------------------------ //
				// ------------------------------------------ //
 
 
				// I represent a single lazy-load image.
				function LazyImage( element ) {
 
					// I am the interpolated LAZY SRC attribute of
					// the image as reported by AngularJS.
					var source = null;
 
					// I determine if the image has already been
					// rendered (ie, that it has been exposed to the
					// viewport and the source had been loaded).
					var isRendered = false;
 
					// I am the cached height of the element. We are
					// going to assume that the image doesn't change
					// height over time.
					var height = null;
 
 
					// ---
					// PUBLIC METHODS.
					// ---
 
 
					// I determine if the element is above the given
					// fold of the page.
					function isVisible( topFoldOffset, bottomFoldOffset ) {
 
						// If the element is not visible because it
						// is hidden, don't bother testing it.
						if ( ! element.is( ":visible" ) ) {
 
							return( false );
 
						}
 
						// If the height has not yet been calculated,
						// the cache it for the duration of the page.
						if ( height === null ) {
 
							height = element.height();
 
						}
 
						// Update the dimensions of the element.
						var top = element.offset().top;
						var bottom = ( top + height );
 
						// Return true if the element is:
						// 1. The top offset is in view.
						// 2. The bottom offset is in view.
						// 3. The element is overlapping the viewport.
						return(
								(
									( top <= bottomFoldOffset ) &&
									( top >= topFoldOffset )
								)
							||
								(
									( bottom <= bottomFoldOffset ) &&
									( bottom >= topFoldOffset )
								)
							||
								(
									( top <= topFoldOffset ) &&
									( bottom >= bottomFoldOffset )
								)
						);
 
					}
 
 
					// I move the cached source into the live source.
					function render() {
 
						isRendered = true;
 
						renderSource();
 
					}
 
 
					// I set the interpolated source value reported
					// by the directive / AngularJS.
					function setSource( newSource ) {
 
						source = newSource;
 
						if ( isRendered ) {
 
							renderSource();
 
						}
 
					}
 
 
					// ---
					// PRIVATE METHODS.
					// ---
 
 
					// I load the lazy source value into the actual
					// source value of the image element.
					function renderSource() {
 
						element[ 0 ].src = source;
 
					}
 
 
					// Return the public API.
					return({
						isVisible: isVisible,
						render: render,
						setSource: setSource
					});
 
				}
 
 
				// ------------------------------------------ //
				// ------------------------------------------ //
 
 
				// I bind the UI events to the scope.
				function link( $scope, element, attributes ) {
 
					var lazyImage = new LazyImage( element );
 
					// Start watching the image for changes in its
					// visibility.
					lazyLoader.addImage( lazyImage );
 
 
					// Since the lazy-src will likely need some sort
					// of string interpolation, we don't want to
					attributes.$observe(
						"bnLazySrc",
						function( newSource ) {
 
							lazyImage.setSource( newSource );
 
						}
					);
 
 
					// When the scope is destroyed, we need to remove
					// the image from the render queue.
					$scope.$on(
						"$destroy",
						function() {
 
							lazyLoader.removeImage( lazyImage );
 
						}
					);
 
				}
 
 
				// Return the directive configuration.
				return({
					link: link,
					restrict: "A"
				});
 
			}
		);
              
            
!
999px

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