Create custom theme features with theme feature support

basic-usage.php

<?php
/**
 * Basic Theme Support usage. Add this to your functions.php file
 */
add_theme_support( 'custom-footer-text' );

/**
 * Elsewhere in your theme...
 */
if( current_theme_supports( 'custom-footer-text' ) ) {
	echo 'Custom Footer Text!';
}

custom-theme-feature-support.php

<?php
/**
 * Determines, whether the specific theme feature is actually supported. Place this in your plugin file.
 * 
 * @link https://github.com/zamoose/themehookalliance/blob/master/tha-theme-hooks.php
 * 
 * @param bool $bool true
 * @param array $args The hook type being checked
 * @param array $registered All registered hook types
 * 
 * @return bool
 */
if( ! function_exists( 'jdn_toolkit_current_theme_supports' ) ) {
	function jdn_toolkit_current_theme_supports( $bool, $args, $registered ) {
		if( isset( $args[0] ) && isset( $registered[0] ) ) {
			return in_array( $args[0], $registered[0] );
		} else {
			return false;
		}
	}
}
add_filter( 'current_theme_supports-jdn-toolkit', 'jdn_toolkit_current_theme_supports', 10, 3 );

require-if-theme-supports-custom-feature.php

<?php
/**
 * Checks a theme's support for a given feature before loading the functions which implement it.
 *
 * @param string $feature The feature being checked.
 * @param string $include Path to the file.
 * @return bool True if the current theme supports the supplied feature, false otherwise.
 */
if( !function_exists( 'require_if_jdn_toolkit_supports' ) ) {
	function require_if_jdn_toolkit_supports( $feature, $include ) {
		if( current_theme_supports( 'jdn-toolkit', $feature ) ) {
			require ( $include );
			return true;
		}
		return false;
	}
}

/**
 * Usage
 */
require_if_jdn_toolkit_supports( 'theme-options', 'path/to/file.php' );

update-current-theme-supports.php

<?php
/**
 * Add theme support to your function.php file
 */
add_theme_support( 'jdn-toolkit', array( 'theme-options', 'portfolio', 'custom-footer-text' ) );

/**
 * Elsewhere in your theme...
 */
if( current_theme_supports( 'jdn-toolkit', 'custom-footer-text' ) {
	echo 'Custom Footer Text!';
}