_comment.rb

= link_to(comment_create_comment_vote_path(@comment, :comment_vote => { :comment_id => @comment.id, :user_id => current_user.id, :vote_flag => true }), {:method => :post, :remote => true, :class => 'like-comment'}) do
  %i.icon-thumbs-up
  %span.helpful-text Mark helpful

comment_votes_controller.rb

class CommentVotesController < ApplicationController
  load_and_authorize_resource

  def create
    @vote = CommentVote.new(params[:comment_vote])
    @vote.save
    respond_to do |format|  
      format.html { redirect_to(@vote) }  
      format.js { render :json =>  @vote, :status => :created, :location => @vote }
    end
  end
end

whatever.js

  $('.like-comment').on('ajax:success', function(event, xhr, data, status) {
    console.log(event, xhr, data, status);
    $(this).removeClass('like-comment').addClass('unlike-comment')
      .children('.helpful-text').text('You marked helpful');
  });