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The OnClientValidationFailed client-side event occurs after a validation for selected file has failed either due to invalid file size or invalid extension

The event handler receives two parameters:

  1. The instance of the RadAsyncUpload control firing the event.

  2. An eventArgs parameter containing the following methods:

  • get_fileName returns the name of the file whose validation has failed

  • get_row returns the upload row for which the event was fired.

One useful case that can be applied in this event is getting information if the validation is triggered by the size of the file or by its extension:

<telerik:RadAsyncUpload RenderMode="Lightweight" runat="server" ID="RadAsyncUpload1" OnClientValidationFailed="OnClientValidationFailed"></telerik:RadAsyncUpload>
function OnClientValidationFailed(sender, args) {
    var fileExtention = args.get_fileName().substring(args.get_fileName().lastIndexOf('.') + 1, args.get_fileName().length);
    if (args.get_fileName().lastIndexOf('.')!=-1) {//this checks if the extension is correct
        if (sender.get_allowedFileExtensions().indexOf(fileExtention)==-1) {
            alert("Wrong Extension!");
        else {
            alert("Wrong file size!");
    else {
        alert("not correct extension!");
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