The onbeforeunload way with turbolinks.

gistfile1.js

// Without turbolinks, it works fine!
$(document).ready(function(){
   formmodified=0;
    $('form *').change(function(){
        formmodified=1;
    });
    window.onbeforeunload = confirmExit;
    function confirmExit() {
        if (formmodified == 1) {
            return "資料有做修改，確定直接離開頁面嗎？";
        }
    }
    $("input[name='commit']").click(function() {
        formmodified = 0;
    });
});

// With turbolinks, we try this...  But got failed...

$(document).on('ready page:load',function(){
  formmodified=0;
  $('form *').change(function(){
    formmodified=1;
  });
  $(window).on('page:before-change', confirmExit);
  function confirmExit() {
    if (formmodified == 1) {
        return "資料有做修改，確定直接離開頁面嗎？";
    }
  }
  $("input[name='commit']").click(function() {
      formmodified = 0;
  });
});