$scope.imageDataUrl

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

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