jimbo2150

This plugin extends the WP_Scripts class, adding some additional methods and filters that overload the existing script output to add Require.js syntax. It loads scripts via Require.js and by default defers until the DOMContentLoaded event fires (unless a manually added require() is called within the head/body and does not wait for the DOM to be loaded. 
It is designed to work in conjunction with HTTP/2 but will function fine without it (though you may see slower load times).
This plugin is design to assist developers in updating and creating JavaScript that is asynchronous – that is, scripts that can load in a different order and do not assume that their dependencies are available immediately. Use of the Asynchronous Module Definition (AMD) allows a script to define it’s dependencies and have them loaded asynchronously prior to the entire script or the initialization portion executes.
It is common for larger projects to concatenate together scripts however, they can end up a jumbled mess and smaller required functions are often duplicated (and redundant) across multiple scripts. HTTP/2 corrects this by allowing multiple resource files to be requested and downloaded within a single TCP window. As projects get larger and more diverse it is becoming more economical to load the individual components (modules) that are needed rather than download and execute one massive concatenated script file (which can also cause the browser to freeze up).
NOTE: This plugin currently only replaces non-administrative (front-end) scripts with Require.js syntax.
Plugin website: https://techie-jim.net/wordpress-plugins/requirewp/

RequireWP

Uses Require.js to load scripts faster and speed up WordPress / increase site load speed & performance. Designed to work with HTTP/2.

Aleksandar Urošević

TechWebUX

Head & Footer Code plugin helps you add custom code snippets (JavaScript, CSS, or HTML) to the page even if you are not a programmer. It could be within the <code><head></code> (site verification code for various services, custom styles, meta or Webfont link), right after opening <code><body></code> (pixel tracking, analytics or heatmap code) or just before closing <code></body></code> tag.
Go to Tools → Head & Footer Code in WordPress Dashboard. Insert custom code to HEAD, BODY or FOOTER section (depending on what you have to do).
All magic is done by hooking to WordPress hooks <code>wp_head</code>, <code>wp_footer</code> and <code>wp_body_open</code>.
<blockquote>
💡 Trial Head & Footer Code plugin on a free dummy website before you add it on your project: <a href="https://tastewp.com/new/?pre-installed-plugin-slug=head-footer-code" rel="nofollow ugc">Test It Now!</a>
</blockquote>
Various code snippets are supported, including but not limited to:
<ul>
<li>Google Analytics 4</li>
<li>Google Tag Manager</li>
<li>Google Ads Conversion</li>
<li>Lite Analytics</li>
<li>Facebook/Meta Pixel</li>
<li>Hotjar</li>
<li>FullStory</li>
<li>Google site verification</li>
<li>Bing site verification</li>
<li>Yandex site verification</li>
<li>Alexa site verification</li>
</ul>
<h3>Homepage in Blog Posts mode</h3>
If your WordPress shows the latest blog posts on the homepage, you can also add specific code only for the homepage on Tools → Head & Footer Code (there will be section Head, body and footer code on Homepage in Blog Posts mode)
<h3>Article specific code</h3>
To insert custom code specific for individual article (post, page or custom post type), use article-specific Metabox while editing post/page/custom post type (check out <a href="https://wordpress.org/plugins/head-footer-code/#screenshots" rel="ugc">Screenshots</a>). There choose if that specific code appends to site-wide code defined on Tools → Head & Footer Code, or to replace it.
<h3>Category specific code</h3>
You can also define a Category specific code on each individual category.
Other taxonomies (tag and custom taxonomy) do not have available their specific code, but for them a Global code is used instead.
<h3>Video guide</h3>
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/Gd41Dv09UC4?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
<h3>Do you need our support?</h3>
If Head & Footer Code does not work on your project, please let us know by <a href="https://wordpress.org/support/plugin/head-footer-code/#new-topic-0" rel="ugc">raising a new support ticket</a> in the <a href="https://wordpress.org/support/plugin/head-footer-code/" rel="ugc">Community Forum</a> and describe what does not works and how to reproduce the issue. We will make sure to resolve the issue as soon as possible.
If you find Head & Footer Code useful for your project, please <a href="https://wordpress.org/support/plugin/head-footer-code/reviews/#new-post" rel="ugc">review plugin</a>.
<h3>Features</h3>
<ul>
<li>Multisite and PHP 8.5 compatible!</li>
<li>Set site-wide custom content for:
<ul>
<li>head page section (before the <code></head></code>)</li>
<li>body section (after the <code><body></code>) – Requires WordPress 5.2!</li>
<li>footer page section (before the <code></body></code>)</li>
</ul>
</li>
<li>Homepage in Blog Posts mode:
<ul>
<li>set homepage specific custom code for head, body and/or footer</li>
<li>toggle homepage specific custom code on paged Homepage (page 2, 3, a nd so on)</li>
</ul>
</li>
<li>Set article specific custom code for:
<ul>
<li>head page section (before the <code></head></code>)</li>
<li>body section (after the <code><body></code>) – Requires WordPress 5.2!</li>
<li>footer page section (before the <code></body></code>)</li>
</ul>
</li>
<li>Set category specific custom code for head, body and/or footer of the page</li>
<li>Choose priority of printed custom code to head/body/footer sections (lower number mean far from <code></head></code> and <code></body></code> and closer to <code><body></code>, higher number means closer to <code></head></code> and <code></body></code> and farther to <code><body></code>)</li>
<li>Choose which post types will have enabled article specific head/body/footer fields</li>
<li>Choose should article specific head/body/footer code be appended to site-wide code, or will replace site-wide code</li>
<li>View on Posts/Pages/Custom Post Types listing if article has defined any article specific custom code</li>
<li>Site-wide section is located under Tools > Head & Footer Code</li>
<li>If you have set WP_DEBUG constant in <code>wp-config.php</code> to <code>true</code>, you’ll see site-wide and article specific entries in page source code wrapped to comments.</li>
<li>[NEW] allow unprivileged user roles Editor and Author to manage article-specific code on single site and multisite (disabled by default)</li>
</ul>
<h3>Data stored in database</h3>
General settings (HEAD, BODY, FOOTER global code and priority, Homepage code and behaviour) saves in WordPress option <code>auhfc_settings</code>. 
Each post/page/custom post type specific HEAD, BODY and FOOTER code and behaviour saves to post meta <code>_auhfc</code>. 
Each category specific HEAD, BODY and FOOTER code and behaviour saves to taxonomy meta <code>_auhfc</code>.
During the Uninstall process all these data has been deleted from the database. 
In case you wish to reinstall plugin, DO NOT UNINSTALL IT although Deactivate, then delete the directory <code>/wp-content/plugins/head-footer-code</code> and then reinstall plugin.
<h3>Permissions on Multisite WordPress</h3>
<ol>
<li>Access to Global: only Super Admin and Administrator</li>
<li>Access to Article specific: Super Admin, Administrator; optional: Editor and Author</li>
<li>Access to Category specific: only Super Admin and Administrator</li>
</ol>

Head & Footer Code

This plugin is what exactly I'm looking for to add custom javascript and CSS codes to specific pages without inserting them inside the template.

A must have plugin

Easy add site-wide, category and article specific custom code before the closing </head> and </body>, or after opening <body> tag.

RequireWP vs Head & Footer Code