http://stackoverflow.com/questions/16723877/jquery-file-upload-maxnumberoffiles-and-getnumberoffiles-options

I believe getNumberOfFiles was only added as an option to a recent version of jquery.fileupload-ui.js (8.2.1).

As an alternative, you can set the option singleFileUploads to false, and in the add callback you can throw errors if more than one file is added.

var maxFiles = 1;

$('#fileupload').fileupload({

    singleFileUploads: false,

    url: '/uploadUrl'

}).bind('fileuploadadd', function (e, data) {

    var fileCount = data.files.length;

    if (fileCount > maxFiles) {

    alert("The max number of files is "+maxFiles);

    return false;

}

});