问如何定义一个方法来监控页面上的内容变化？

EN

class UsersController < ApplicationController
  before_action :signed_in_user, only: [:edit, :update]
  before_action :correct_user,   only: [:edit, :update]
  before_action :admin_user,     only: [:index, :destroy]

  def show
    @user = User.find(params[:id])
    @microposts = @user.microposts.paginate(page: params[:page])
  end

  def new
    @user = User.new
  end

  def index
    @users = User.paginate(page: params[:page])    
  end

  def create
    @user = User.new(user_params)
    if @user.save
      sign_in @user
      flash[:success] = "Welcome to the MatchCenter Alpha Test!"    
      redirect_to root_path
    else
      render 'new'
    end
  end


  def show
    @user = User.find(params[:id])

  end


  def admin_user
      redirect_to(root_url) unless current_user.admin?
  end

  def edit
    @user = User.find(params[:id])
  end

  def destroy
    User.find(params[:id]).destroy
    flash[:success] = "User deleted."
    redirect_to users_url
  end

  def update
    @user = User.find(params[:id])
    if @user.update_attributes(user_params)
      flash[:success] = "Profile updated"
      redirect_to @user
    else
      render 'edit'
    end

  end


  private

    def user_params
      params.require(:user).permit(:name, :email, :password,
                                   :password_confirmation)
    end

    # Before filters

    def correct_user
      @user = User.find(params[:id])
      redirect_to(root_url) unless current_user?(@user)
    end
end

class MicropostsController < ApplicationController
  before_action :signed_in_user
  before_action :correct_user,   only: :destroy

  def new 
    @micropost = current_user.microposts.build
  end

  def create
    @micropost = current_user.microposts.build(micropost_params)
    if @micropost.save
      flash[:success] = "Sweet! The item has been added to your watch list, and we'll notify you whenever matches are found."
      redirect_to buy_path
    else
      render 'static_pages/home'
    end
  end

  def destroy
    @micropost.destroy
    redirect_to buy_path
  end

  private

    def micropost_params
      params.require(:micropost).permit(:keyword, :min, :max, :condition)
    end

    def correct_user
      @micropost = current_user.microposts.find_by(id: params[:id])
      redirect_to root_url if @micropost.nil?
    end
end