submit.js

$(function() {
  $('#id-do-form').submit(function() {  
    var valuesToSubmit = $(this).serialize();
    $.ajax({
        type: "POST",
        url: $(this).attr('action'), //sumbits it to the given url of the form
        data: valuesToSubmit,
        dataType: "JSON" // you want a difference between normal and ajax-calls, and json is standard
    }).success(function(json){
        console.log("success", json);
    });
    return false; // prevents normal behaviour
  }); 
);