Rails用Google Tag Manager ViewHelper

gtm_helper.rb

module GtmHelper
  GTM_SCRIPT = "(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':" \
             "new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0]," \
             "j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=" \
             "'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);" \
             "})(window,document,'script','dataLayer','%s');".freeze
  GTM_IFRAME_URL = "https://www.googletagmanager.com/ns.html?id=%s".freeze

  def gtm_key = @gtm_key ||= Rails.application.config_for(:gtm)["key"] || "SET_GTM_KEY"
  def render_gtm_head = tag.script(GTM_SCRIPT % gtm_key, escape: false)
  def render_gtm_body = tag.noscript(tag.iframe(nil, src: GTM_IFRAME_URL % gtm_key, height: 0, width: 0, style: "display:none;visibility:hidden"))
end