Ruby on Rails

Application.js is not evaluated in the context of any session variables or methods. The simplest way to access username from javascript would be to set a cookie in a before_action on application controller:

class ApplicationController < ActionController::Base    before_action :set_user      private      def set_user      cookies[:username] = current_user.name || 'guest'    end  end

Then from any js in app/assets you can access the cookie:

alert(document.cookie);

A more verbose but arguably cleaner method would be to create a route that accesses the current user and returns the username e.g.

routes.rb

get 'current_user' => "users#current_user"

users_controller.rb

def current_user      render json: {name: current_user.name}  end

application.js

$.get('/current_user', function(result){    alert(result.name);  });