This code helps you to implement lazy loading of images in an Angular application. Lazy loading is a technique used to delay the loading of images until they are actually needed, reducing the initial page load time and improving performance.
In this code, an Angular application module is created, along with a controller that manages the visibility and manipulation of a set of images. The code also includes a directive called “bnLazySrc” that handles the lazy loading functionality by monitoring the visibility of images on the page and rendering them when necessary.
By using this code, you can optimize your Angular application by loading images only when they are in the viewport, providing a smoother user experience.
How to Create Lazy Loading Images In AngularJS
Create the HTML structure for lazy loading images as follows:
<div ng-app="Demo" ng-controller="AppController">
<h2>
Lazy Loading Images With AngularJS
</h2>
<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>
<div>
Style the gallery using the following CSS styles:
/* 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");
}
Now, load the jQuery and AngularJS by adding the following CDN links before closing the body tag:
<script src='//cdnjs.cloudflare.com/ajax/libs/jquery/2.1.3/jquery.min.js'></script> <script src='https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.2.1/angular.min.js'></script>
Finally, use the following JavaScript code. To insert your own images into the code, you would need to modify the buildPhotoSet() function within the controller (AppController). This function is responsible for creating a set of photos with unique source (SRC) values.
// 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"
});
}
);
Remember to update the number of images you want to load by adjusting the size parameter when calling buildPhotoSet() in the controller.
That’s all! hopefully, you have successfully created lazy loading images in your Angular project. If you have any questions or suggestions, feel free to comment below.
