js.rb

require 'json'

COUNTRY_CODES = %w[AF BR US NO CN RU AU NZ MX IN BD IR NG SA ZA FR]

Thread.new do
  loop do
    sleep 1   
    set_json
  end
end

def set_json
  temp_json = {}
  COUNTRY_CODES.each { |c| temp_json[c] = rand(1..2500) }
  write_to_json temp_json
end

def write_to_json(json)
  File.open("visitors.json", "w") do |f|
    f.write(json.to_json)
  end
  puts "Wrote new json"
end