The scope in AngularJS fails to detect changes

One common issue I encountered involved the $scope field used for the ng-src attribute within an <img>:

$scope.imageDataUrl

To initialize this field, I utilized the following code:

$scope.myJsWrapper = new MyJsWrapper();
$scope.myJsWrapper.getImageUrl(function (imageDataUrl) {
    $scope.imageDataUrl = imageDataUrl;
});

The external JS function responsible for this process is outlined below:

function MyJsWrapper() {
    this.getImageUrl = function (withImage) {
        thirdPartyJsFile.getData().then(function (data) {
            var imageDataUrl = thirdPartyJsFile.getDataUrl(data, "image/png");
            if (withImage) {
                withImage(imageDataUrl);
            }
         });
    }
}

This approach might be convoluted, but it was necessitated by the requirements of the third-party application. The main issue arises from Angular's failure to detect changes in the imageDataUrl field, resulting in the image not being updated. Though I attempted using $scope.$watch for monitoring changes, it failed to trigger as expected. Interestingly, the field only updates when browser scrolling or clicking occurs (including the $scope.$watch). Hence, my primary question pertains to why Angular fails to recognize these changes and what measures must be taken for correction.

Answer №1

To ensure that changes made by a third-party library are recognized by Angular, you must call $scope.$apply().

$scope.$apply(function() {
    $scope.imageDataUrl = imageDataUrl;
});

Include this in your callback function.

For more information, refer to the official documentation.

$apply() allows execution of an expression in AngularJS from external sources such as browser DOM events, setTimeout, XHR, or third-party libraries. To ensure proper scope lifecycle management, exception handling, and watch execution, calling into the AngularJS framework is required.

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