Klaylton Fernando

This plugin adds 3 fields on every page and blog post where you can type your code in a readable interface.
In addition to being very light and functional, the WP Custom Code plugin also allows you to work with external libraries. Basque paste the address 
of the javascript library of your choice in the designated field and you will be able to enjoy this indispensable resource.

WP Custom Code

Add CSS and Javascript to your pages simply and quickly. WP Custom Code supports CodeMirror.

k0tik

The usual Text widget allows you to insert arbitrary Text and/or HTML code. This allows that too, but also parses any PHP or JavaScript code in the text widget and executes it.
This plugin is based on “PHP Code Widget”, but now available for use by site administrators ONLY, which makes it more secure.
All PHP code must be enclosed in the standard php opening and closing tags ( <code><?php</code> and <code>?></code> ) for it to be recognized and executed. Also JavaScript code must be enclosed in the <code><script></code> and <code></script></code> tags, as usual.

Safe PHP Code Widget

Adds a secure and simple widget in which you can use PHP and JavaScript code. Also you can use unfiltered HTML or just Text. Admin Use Only.

WP Custom Code vs Safe PHP Code Widget