Wait for AngularJS to load when the background image of a div becomes visible

Question

Wait for AngularJS to load when the background image of a div becomes visible

Currently, I am utilizing the ng-repeat feature to fetch data from a $http.post request and then save it to the $scope.data variable.

<div ng-repeat="key in [] | range:data.pages">
    <div class="pageBackground" id="page_{{ (key+1) }}" ng-style="{'background-image':'url(/images/{{data.id}}/{{(key+1)}}.png)'}">
    <!-- more content here -->
</div>

The issue I'm encountering is that the .pageBackground class tends to load prior to the background image appearing on the screen. My goal is to prevent anything from showing up until the background-image has been successfully loaded, but so far, I haven't found a solution for this problem.

Could anyone offer some advice or suggestions on how to achieve this? Thank you!

javascript html css angularjs

Answer 1

Answer №1

It seems like finding a definitive solution to your issue may be challenging. One workaround could involve utilizing the Image object, as detailed in this response. An example of this approach could be through a directive:

angular.module("yourModule").directive("showOnceBackgroundLoaded", [function () {
  return {
    restrict: "A",
    scope: false,
    link: function (scope, element, attributes) {
      element.addClass("ng-hide");
      var image = new Image();
      image.onload = function () {
        // The browser likely cached the image, enabling quick loading
        scope.$apply(function () {
          element.css({ backgroundImage: 'url("' + attributes.showOnceBackgroundLoaded + '")' });
          element.removeClass("ng-hide");
        });
      };
      image.src = attributes.showOnceBackgroundLoaded;
    }
  };
}]);

To implement this, you can use:

<div ng-repeat="key in [] | range:data.pages">
    <div class="pageBackground" id="page_{{ (key+1) }}" show-once-background-loaded="/images/{{data.id}}/{{(key+1)}}.png">
    <!-- Add any necessary content here -->
</div>

Answer 2

It seems like finding a definitive solution to your issue may be challenging. One workaround could involve utilizing the Image object, as detailed in this response. An example of this approach could be through a directive:

angular.module("yourModule").directive("showOnceBackgroundLoaded", [function () {
  return {
    restrict: "A",
    scope: false,
    link: function (scope, element, attributes) {
      element.addClass("ng-hide");
      var image = new Image();
      image.onload = function () {
        // The browser likely cached the image, enabling quick loading
        scope.$apply(function () {
          element.css({ backgroundImage: 'url("' + attributes.showOnceBackgroundLoaded + '")' });
          element.removeClass("ng-hide");
        });
      };
      image.src = attributes.showOnceBackgroundLoaded;
    }
  };
}]);

To implement this, you can use:

<div ng-repeat="key in [] | range:data.pages">
    <div class="pageBackground" id="page_{{ (key+1) }}" show-once-background-loaded="/images/{{data.id}}/{{(key+1)}}.png">
    <!-- Add any necessary content here -->
</div>

Answer 3

Answer №2

Check out this helpful solution:

Is there a way to determine when a CSS background image has finished loading?

The trick is to create a hidden duplicate element that loads the same image. Only when that duplicate image has fully loaded (using the onload event) should you display your desired element, like so:

<div ng-repeat="key in [] | range:data.pages" ng-init="_imageLoaded={}">
    <div ng-show="_imageLoaded[$index]" class="pageBackground" id="page_{{ (key+1) }}" ng-style="{'background-image':'url(/images/{{data.id}}/{{(key+1)}}.png)'}">
    <img ng-show="false" src="/images/{{data.id}}/{{(key+1)}}.png" onload="_imageLoaded[$index] = true;" />
    <!-- additional content goes here -->
</div>

Answer 4

Check out this helpful solution:

Is there a way to determine when a CSS background image has finished loading?

The trick is to create a hidden duplicate element that loads the same image. Only when that duplicate image has fully loaded (using the onload event) should you display your desired element, like so:

<div ng-repeat="key in [] | range:data.pages" ng-init="_imageLoaded={}">
    <div ng-show="_imageLoaded[$index]" class="pageBackground" id="page_{{ (key+1) }}" ng-style="{'background-image':'url(/images/{{data.id}}/{{(key+1)}}.png)'}">
    <img ng-show="false" src="/images/{{data.id}}/{{(key+1)}}.png" onload="_imageLoaded[$index] = true;" />
    <!-- additional content goes here -->
</div>

Answer 5

Answer №3

If you want to wait for the image to load before running your startup function, follow this code snippet:

  var picture = new Image();
  picture.onload = function(){
    fetchInformation();
  };
  picture.src = 'https://example.com/image.jpg';

Once the image has loaded, set an ng-if="pictureLoaded" in your HTML and change its value to true within the fetchInformation function.

Answer 6

If you want to wait for the image to load before running your startup function, follow this code snippet:

  var picture = new Image();
  picture.onload = function(){
    fetchInformation();
  };
  picture.src = 'https://example.com/image.jpg';

Once the image has loaded, set an ng-if="pictureLoaded" in your HTML and change its value to true within the fetchInformation function.

Answer 7

Answer №4

Presented here is a directive that integrates your image as a background, and only reveals itself once the image has fully loaded. The "mysrc" parameter allows for the inclusion of variables to create various images (such as when using ng-repeat).

angular.module('foo', [])
  .directive('myPageBackground', function() {
    return {
      scope: {
        key: '=', // used as the element's ID; omit if set externally
        mysrc: '=' // URL for the desired background image
      },
      template: '<div ng-show="showMe" class="pageBackground" id="page_{{key}}" ng-style="{\'background-image\':\'url({{mysrc}})\'}"></div>',
      link: function(scope) {
        var img = new Image();
        img.onload = function() {
          scope.showMe = true;
          scope.$apply();
        };
        img.src = scope.mysrc;
      }
    }
  });

.pageBackground {
  width: 200px; height: 200px;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="foo">
  <!-- Demonstrating with hardcoded values for demo purposes only: -->
  <div my-page-background key="'1'" mysrc="'http://placehold.it/200x200'"></div>
  <div my-page-background key="'2'" mysrc="'http://placehold.it/150x150'"></div>
  <div my-page-background key="'3'" mysrc="'http://placehold.it/100x100'"></div>
</div>

Answer 8

Presented here is a directive that integrates your image as a background, and only reveals itself once the image has fully loaded. The "mysrc" parameter allows for the inclusion of variables to create various images (such as when using ng-repeat).

angular.module('foo', [])
  .directive('myPageBackground', function() {
    return {
      scope: {
        key: '=', // used as the element's ID; omit if set externally
        mysrc: '=' // URL for the desired background image
      },
      template: '<div ng-show="showMe" class="pageBackground" id="page_{{key}}" ng-style="{\'background-image\':\'url({{mysrc}})\'}"></div>',
      link: function(scope) {
        var img = new Image();
        img.onload = function() {
          scope.showMe = true;
          scope.$apply();
        };
        img.src = scope.mysrc;
      }
    }
  });

.pageBackground {
  width: 200px; height: 200px;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app="foo">
  <!-- Demonstrating with hardcoded values for demo purposes only: -->
  <div my-page-background key="'1'" mysrc="'http://placehold.it/200x200'"></div>
  <div my-page-background key="'2'" mysrc="'http://placehold.it/150x150'"></div>
  <div my-page-background key="'3'" mysrc="'http://placehold.it/100x100'"></div>
</div>

Answer 9

Answer №5

Using the same class="pageBackground" will result in having the same background image every time. To avoid this, you can preload the image so that the browser caches it:

<img src="url" style="display:none;"/>

Another option is to use Javascript to preload the image when the page loads:

var img = new Image();
img.src = 'some url';

Since the post is likely triggered by user interaction, the image will already be loaded in the browser and will appear immediately when applying class="pageBackground".

I hope this explanation helps!

Answer 10

Using the same class="pageBackground" will result in having the same background image every time. To avoid this, you can preload the image so that the browser caches it:

<img src="url" style="display:none;"/>

Another option is to use Javascript to preload the image when the page loads:

var img = new Image();
img.src = 'some url';

Since the post is likely triggered by user interaction, the image will already be loaded in the browser and will appear immediately when applying class="pageBackground".

I hope this explanation helps!

Answer 11

Answer №6

Why not consider using the ngSrc directive instead of a div for your solution? Another option to explore could be implementing a lightweight lazy loading image library like ng-lazy-img.

I trust this suggestion will prove useful in your endeavors!

Answer 12

Why not consider using the ngSrc directive instead of a div for your solution? Another option to explore could be implementing a lightweight lazy loading image library like ng-lazy-img.

I trust this suggestion will prove useful in your endeavors!

Answer 13

Answer №7

Check out this fully operational example showcasing the use of the Image object.

function CustomCtrl($scope) {
  $scope.pictures = [{
    source: 'https://farm4.staticflickr.com/3261/2801924702_ffbdeda927_d.jpg'
  }, {
    source: 'https://farm9.staticflickr.com/8455/8048926748_1bc624e5c9_d.jpg'
  }];
  angular.forEach($scope.pictures, function(picture) {
    var img = new Image();
    img.onload = function() {
      $scope.$apply(function() {
        picture.changedSrc = picture.source;
      });
    };
    img.src = picture.source;
  });
}

.customStyle {
  color: purple;
  padding: 10px;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app>
  <div ng-controller="CustomCtrl">
    <div ng-repeat="picture in pictures" ng-class="{ customStyle: !!picture.changedSrc }" style="background-image: url({{picture.changedSrc}})">
      <h2>NEW TEXT GOES HERE</h2>
      <p>
        This is sample text for demonstration purposes.
      </p>
    </div>
  </div>
</div>

Feel free to modify this example to fit your needs.

Answer 14

Check out this fully operational example showcasing the use of the Image object.

function CustomCtrl($scope) {
  $scope.pictures = [{
    source: 'https://farm4.staticflickr.com/3261/2801924702_ffbdeda927_d.jpg'
  }, {
    source: 'https://farm9.staticflickr.com/8455/8048926748_1bc624e5c9_d.jpg'
  }];
  angular.forEach($scope.pictures, function(picture) {
    var img = new Image();
    img.onload = function() {
      $scope.$apply(function() {
        picture.changedSrc = picture.source;
      });
    };
    img.src = picture.source;
  });
}

.customStyle {
  color: purple;
  padding: 10px;
}

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<div ng-app>
  <div ng-controller="CustomCtrl">
    <div ng-repeat="picture in pictures" ng-class="{ customStyle: !!picture.changedSrc }" style="background-image: url({{picture.changedSrc}})">
      <h2>NEW TEXT GOES HERE</h2>
      <p>
        This is sample text for demonstration purposes.
      </p>
    </div>
  </div>
</div>

Feel free to modify this example to fit your needs.

Answer 15

Answer №8

An efficient way to handle image loading in Angular is by using promises. Only render the view once the image has been successfully loaded as promised.

Have you reviewed the following resource?

preloading-images-in-angularjs

Thank you.

Answer 16

An efficient way to handle image loading in Angular is by using promises. Only render the view once the image has been successfully loaded as promised.

Have you reviewed the following resource?

preloading-images-in-angularjs

Thank you.

Wait for AngularJS to load when the background image of a div becomes visible

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

Answer №7

Answer №8

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