Vladimir Prelovac

<p>The Yahoo! Exceptional Performance team recommends <a href="http://developer.yahoo.com/performance/rules.html#js_bottom" rel="nofollow ugc">placing scripts at the bottom of your page</a> because of the way browsers download components.</p>
<p>“The problem caused by scripts is that they block parallel downloads. The HTTP/1.1 specification suggests that browsers download no more than two components in parallel per hostname. If you serve your images from multiple hostnames, you can get more than two downloads to occur in parallel. While a script is downloading, however, the browser won’t start any other downloads, even on different hostnames.</p>
<p>In some situations it’s not easy to move scripts to the bottom. If, for example, the script uses document.write to insert part of the page’s content, it can’t be moved lower in the page. There might also be scoping issues. In many cases, there are ways to workaround these situations.”</p>
<p>WordPress default behavior is to load javascript in the  page.</p>
<p>This plugin will move all javascript code to the footer if the plugins have <a href="http://www.prelovac.com/vladimir/best-practice-for-adding-javascript-code-to-wordpress-plugin" rel="nofollow ugc">declared javascript properly</a>.</p>
<p>Plugin by <a href="http://www.prelovac.com/vladimir" rel="nofollow ugc">Vladimir Prelovac</a>. Looking for <a href="http://www.prelovac.com/vladimir/services" rel="nofollow ugc">WordPress Services</a>?</p>
<h3>License</h3>
<p>This file is part of Footer JavaScript.</p>
<p>Footer JavaScript is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.</p>
<p>Footer JavaScript is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.</p>
<p>You should have received a copy of the GNU General Public License along with Footer JavaScript. If not, see <a href="http://www.gnu.org/licenses/" rel="nofollow ugc">http://www.gnu.org/licenses/</a>.</p>


JavaScript to Footer

I used and face some of bad experience with it 

Can't give perfect result

This plugin automatically moves JavaScript code to page footer, speeding up page loading time.

Anand Kumar

jamify

Digital Liberation

<p>An essential WordPress plugin to easily insert scripts and styles (like Google Analytics, CSS, etc.) into your website’s header and footer.</p>
<p>Looking for a way to add Google Analytics, Facebook Pixel, or custom tracking code to your website’s header or footer?</p>
<p>Header and Footer Scripts is a simple yet powerful plugin that lets you inject code—such as Google Analytics, custom CSS, Facebook Pixel, and chat widgets—directly into your site’s header (<code><head></code>) or footer.</p>
<p>No bloat, no ads. This lightweight plugin simply does what it says: inserts code into your header and footer efficiently.</p>
<p>All you have to do is add the appropriate HTML code.</p>
<p>Don’t forget to wrap your code with proper tags.</p>
<pre><code><script type="text/javascript">
YOUR JS CODE HERE
</script>
</code></pre>
<p>Or for CSS:</p>
<pre><code><style type="text/css">
YOUR CSS CODE HERE
</style>
</code></pre>
<h4>Why use this plugin:</h4>
<ul>
<li>Insert scripts globally into the header and footer of your entire website.</li>
<li>Supports all script types including HTML, JavaScript, and CSS.</li>
<li>Add specific scripts to the header of individual posts or pages.</li>
<li>To insert code to Custom Post Type [New Feature].</li>
</ul>
<p>The plugin should be compatible with WooCommerce.</p>
<h4>What it does not offer</h4>
<ul>
<li>You can’t insert/execute PHP codes.</li>
</ul>
<p>Almost all WordPress themes support this “Header and Footer Scripts” plugin. If the codes are not appearing in your site [ask for support] or look at your theme file if they have standard <code>wp_head</code> and <code>wp_footer</code> hooks.</p>
<h4>Important Links</h4>
<p>For further information you are welcomed to follow these links:</p>
<ul>
<li><strong><a href="https://github.com/anandkumar/header-and-footer-scripts/wiki" rel="nofollow ugc">Read Documentation</a></strong></li>
<li><strong><a href="https://wordpress.org/support/plugin/header-and-footer-scripts/" rel="ugc">Get Support</a></strong></li>
<li><strong><a href="https://github.com/anandkumar/header-and-footer-scripts" rel="nofollow ugc">GitHub Repository</a></strong></li>
</ul>


Header and Footer Scripts

good

Como es posible que al desinstalar el plugin, si no has borrado el script te deje el código ahi metido. Y luego a averiguar de donde vienen los errores. 

Al desinstalar te deja el código

Header and Footer Scripts plugin allows you to add scripts to WordPress site's  and just before closing  tag.

JavaScript to Footer vs Header and Footer Scripts