From 239b70342fb7298686d30ca384870070048b435f Mon Sep 17 00:00:00 2001
From: Alan Guo Xiang Tan <gxtan1990@gmail.com>
Date: Tue, 19 Mar 2024 04:03:49 +0800
Subject: [PATCH] PERF: Remove unnecessary <link rel="preload"> for theme
 javascript (#26220)

This is a follow up to e2da72b76c7f49c2c3a159ce48051c4050f3dc3e.

Why this change?

According to https://web.dev/articles/preload-critical-assets,

> By preloading a certain resource, you are telling the browser that you would like to fetch it sooner than the browser would otherwise discover it because you are certain that it is important for the current page.

The preload resource hint is meant to tell the browser to fetch
resources that it would not discover upfront or early. However, we are
not using it the right way because we are literally adding the resource
hint right before a `<script>` tag which means the browser would have
discovered the resource even without the resource hint.

What does this change do?

This commit removes the preload resource hint which are added right
before script tags since the optimization here is highly questionable at the expense of making
our initial DOM larger.
---
 app/models/theme.rb       | 3 +--
 app/models/theme_field.rb | 2 --
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/app/models/theme.rb b/app/models/theme.rb
index 5a8b66fa3d4..f4b66c16852 100644
--- a/app/models/theme.rb
+++ b/app/models/theme.rb
@@ -6,7 +6,7 @@ require "json_schemer"
 class Theme < ActiveRecord::Base
   include GlobalPath
 
-  BASE_COMPILER_VERSION = 80
+  BASE_COMPILER_VERSION = 81
 
   class SettingsMigrationError < StandardError
   end
@@ -471,7 +471,6 @@ class Theme < ActiveRecord::Base
             .compact
 
         caches.map { |c| <<~HTML.html_safe }.join("\n")
-          <link rel="preload" href="#{c.url}" as="script" nonce="#{ThemeField::CSP_NONCE_PLACEHOLDER}">
           <script defer src="#{c.url}" data-theme-id="#{c.theme_id}" nonce="#{ThemeField::CSP_NONCE_PLACEHOLDER}"></script>
         HTML
       end
diff --git a/app/models/theme_field.rb b/app/models/theme_field.rb
index 38dc09d28f6..5387c9a79da 100644
--- a/app/models/theme_field.rb
+++ b/app/models/theme_field.rb
@@ -191,7 +191,6 @@ class ThemeField < ActiveRecord::Base
     javascript_cache.save!
 
     doc.add_child(<<~HTML.html_safe) if javascript_cache.content.present?
-      <link rel="preload" href="#{javascript_cache.url}" as="script" nonce="#{CSP_NONCE_PLACEHOLDER}">
       <script defer src='#{javascript_cache.url}' data-theme-id='#{theme_id}' nonce="#{CSP_NONCE_PLACEHOLDER}"></script>
     HTML
     [doc.to_s, errors&.join("\n")]
@@ -300,7 +299,6 @@ class ThemeField < ActiveRecord::Base
     javascript_cache.save!
     doc = ""
     doc = <<~HTML.html_safe if javascript_cache.content.present?
-          <link rel="preload" href="#{javascript_cache.url}" as="script" nonce="#{ThemeField::CSP_NONCE_PLACEHOLDER}">
           <script defer src="#{javascript_cache.url}" data-theme-id="#{theme_id}" nonce="#{ThemeField::CSP_NONCE_PLACEHOLDER}"></script>
         HTML
     [doc, errors&.join("\n")]