Rails image upload with carrier wave

I successfully created a form for User model where i can upload image with carrier wave. This works nicely with submit button.

Everything is fine but i want to improve that with jquery file upload or something similar. So my imagination is i will click on file_upload button then select the file and after that it will preview the thumb of image.

I tried to follow railcast #381 but when i upload image, the preview will appear after refresh of page. Is it better to use js response or json? Is there a better way for ajax image upload? Thanks for advices