how to intercept a Grav frontend form using AJAX to avoid page refresh when form submitted

intercept php form submittion via ajax.js

/*
ref: http://stackoverflow.com/questions/12188847/intercept-form-post-string-and-send-via-ajax-instead
*/

how ajax and php forms work:
- http://code.tutsplus.com/tutorials/submit-a-form-without-page-refresh-using-jquery--net-59

follow tutorial on getgrav frontend forms:
- https://learn.getgrav.org/forms/forms

use ajax to intercept form submissiom:
- http://stackoverflow.com/questions/12188847/intercept-form-post-string-and-send-via-ajax-instead