Azure CDN Image Tag Helper Error Handling

azure-cdn-image-error.js

//Retrieve any existing onerror handler code 
var onError = output.Attributes[OnErrorAttributeName] ? .Value as string;
//Check if there's a fallback source and no onerror handler 
if (!string.IsNullOrWhiteSpace(FallbackSrc) && string.IsNullOrWhiteSpace(onError)) {
    string resolvedUrl;
    if (TryResolveUrl(FallbackSrc, out resolvedUrl)) {
        FallbackSrc = resolvedUrl;
    }
    if (AppendVersion) {
        FallbackSrc = _fileVersionProvider.AddFileVersionToPath(FallbackSrc);
    }
    //Apply fallback handler code 
    onError = $ "this.src='{FallbackSrc}';console.log('{Src} NOT FOUND.')";
    output.Attributes.SetAttribute(OnErrorAttributeName, onError);
}