ftp-manager/app/assets/javascripts/main.js

function getPassword($container, password) {
  $container.data('password', password);
  $container.find('span').html(password);
  $container.find('a').detach();
  $container.prepend('<i class="fa fa-unlock fa-lg"></i>');
}

function hidePassword($src){
  $src.siblings('span').html('********');
  $src.removeClass('fa-unlock').addClass('fa-lock');
}

function revealPassword($src){
  $src.siblings('span').html($src.parent().data('password'));
  $src.removeClass('fa-lock').addClass('fa-unlock');
}

$(function(){
  $("[data-id=passwd]").on("ajax:success", "a", function(e, data){
    getPassword($(e.target).parent(), data.hash);
  });

  $("[data-id=passwd]").on('click', 'i', function(){
    if($(this).hasClass('fa-unlock')){
      hidePassword($(this));
    } else {
      revealPassword($(this));
    }
  });
});