How can I diagnose an error in using jQuery file upload?

Question

I am trying to achieve an iframe transport file upload, using the blueimp file upload plugin as follows:

$(jQueryUploadInput).fileupload();
$(jQueryUploadInput).fileupload('send', {
        forceIframeTransport: true,
        fileUpload: profilePicInput,
        url: $.acme.resource.links.editProfilePictureUrl
    })
    .error(function(jqXHR, textStatus, errorThrown) {
        debugger;
    })
    .success(function(result, textStatus, jqXHR) {
        debugger;
    });

When I debug the view that needs the file upload, the debugger call inside my error function is hit, but all three parameters are undefined, as if the error function was invoked for no reason. profilePicInput is a valid file input with one selected file. The action pointed to by $.acme.resource.links.editProfilePictureUrl is a valid action url, but a breakpoint in my controller never even gets hit. I also have no idea how to proceed.

I know the API doc says:

The fileInput property must be a jQuery collection with an input of type file with a valid files selection.

so I have tried both ways of setting the fileUpload option, with the same result.

fileUpload: profilePicInput
fileUpload: $(profilePicInput)

Just BTW, this code is being called inside a view model script, not directly in the view itself, if that might mean or affect anyhting. I don't see how, because the viewmodel script is loaded into the view anyway.

Answer 1

This is a common problem:

• jquery file Upload rails "Error Empty file upload result"
• blueImp/jquery file upload - How do I get the error message if the file type was not accepted?
• Passing the error message to jQuery File Upload
• http://support.cloudinary.com/entries/25570742-How-to-display-error-messages-when-client-side-validation-fails-

The last link advises the following:

processalways: function(e,data){
  if (data.files.error) alert(data.files[0].error);
}

You can also access any of the other Processing Callback Options. See the API.

Any processing failure for an individual file can, for example, also be checked with the processfail callback

function (e, data) {
    console.log('Processing ' + data.files[data.index].name + ' failed.');
}

I hope that answers your question. If I didn't understand your question correctly, please let me know.