<script>
                jQuery(function(){                    
                    var upload = new AjaxUpload(jQuery('#test4'), {
                        action: 'upload-test.php',
                        name: 'woohoo-custom-name',
                        data: {
                            'key1': "This data won't be sent, we will overwrite it."
                        },
                        autoSubmit: false,
                        responseType: 'json',
                        onChange: function(file, ext){
                        },
                        onSubmit: function(file, ext){
                            // Allow only images. You should add security check on the server-side.
                            if (ext && /^(jpg|png|jpeg|gif)$/i.test(ext)) {                            
                                this.setData({
                                    'key1': 'This should be alerted',
                                    'key2': '...'
                                });
                            } else {
                                alert('not image');
                                return false;
                            }                            
                        },
                        onComplete: function(file, response){
                            this.disable();
                            alert(response.post.key1);
                        }
                    });
                    jQuery('#test4upload').click(function(){
                        upload.submit();
                        upload.enable();
                        return false;
                    });
                });                    
            </script>