Also see part 1 of this post

Final result: f

HOWTO:

routes.rb

  resources :posts do
    member do
      patch "upvote", to: "posts#upvote"
      patch "downvote", to: "posts#downvote"
    end
  end

posts/posts_controller.rb

class PostsController < ApplicationController
  def index
    @posts = Post.all.order(cached_votes_score: :desc)
  end

  def upvote
    @post = Post.find(params[:id])
    if current_user.voted_up_on? @post
      @post.unvote_by current_user
    else
      @post.upvote_by current_user
    end
    render "vote.js.erb"
  end

  def downvote
    @post = Post.find(params[:id])
    if current_user.voted_down_on? @post
      @post.unvote_by current_user
    else
      @post.downvote_by current_user
    end
    render "vote.js.erb"
  end

end

posts/index.html.erb

<h1>Posts</h1>
<% @posts.each do |post| %>
  <%= post.name %>
  <% if current_user %>
    <br>
    <%= render 'posts/upvote_link', post: post %>
    <%= render 'posts/like_count', post: post %>
    <%= render 'posts/downvote_link', post: post %>
  <% end %>
  <hr>
<% end %>

posts/_upvote_link.html.erb

<%= content_tag "div", id: "upvote-#{post.id}" do %>
  <%= link_to upvote_post_path(post), method: :patch, remote: true, data: { disable_with: "voting..." } do %>
    <% if current_user.voted_up_on? post %>
      <i class="far fa-thumbs-up" style="color: green;"></i>
      unvote
    <% else %>
      <i class="far fa-thumbs-up"></i>
      upvote
    <% end %>
  <% end %>
<% end %>

posts/_downvote_link.html.erb

<%= content_tag "div", id: "downvote-#{post.id}" do %>
  <%= link_to downvote_post_path(post), method: :patch, remote: true, data: { disable_with: "voting..." } do %>
    <% if current_user.voted_down_on? post %>
      <i class="far fa-thumbs-down" style="color: red;"></i>
      unvote
    <% else %>
      <i class="far fa-thumbs-down"></i>
      downvote
    <% end %>
  <% end %>
<% end %>

posts/_like_count.html.erb

<%= content_tag "div", id: "like-count-#{post.id}" do %>
  <%= post.cached_votes_score %>
<% end %>

posts/vote.js.erb

document.getElementById("like-count-<%= @post.id %>").innerHTML = "<%= j render "posts/like_count", post: @post %>";
document.getElementById("downvote-<%= @post.id %>").innerHTML = "<%= j render "posts/downvote_link", post: @post %>";
document.getElementById("upvote-<%= @post.id %>").innerHTML = "<%= j render "posts/upvote_link", post: @post %>";