Creating Custom Theme Feature Support

Since WordPress version 2.9 theme developers have taken advantage of the add_theme_support feature. Built-in theme features include custom header images, custom backgrounds, post formats, and more. However, we’ve also been given a filter in the current_theme_supports function that allows us to expand theme feature support beyond the built-in options.

The most obvious, and simplest, usage of theme features is to first use add_theme_support to register a feature supported by your theme. Then we can verify the feature is supported with the conditional current_theme_supports function. For example:

	<?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!';
	}

view raw basic-usage.php hosted with ❤ by GitHub

Expanding Custom Theme Features With Arguments

That’s all fine and dandy, but what if you have a lot of potential theme features that could vary depending on the theme? You might be creating a theme extending plugin or theme extension for plugins to use, perhaps. Instead of listing out a ton of add_theme_support declarations (and their conditionals all over the place), let’s simplify it to a single declaration, shall we?

Thanks to the way current_theme_supports is written, we can create a single feature and pass through a multitude of “sub-features” in an array with a second $arguments variable like this: add_theme_support( $feature, $arguments );. In order for this to be useful, however, we’ll need to amend the current_theme_supports function to accept the secondary features, using a feature-specific filter, then we can use it accordingly.

For example, I’m creating a theme extending plugin. Each theme will use a single line to add theme support for a multitude of features. First, we’ll create a function to add the arguments as acceptable values in the current_theme_supports function. Then we’ll add the features to our theme.

	<?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 );

view raw custom-theme-feature-support.php hosted with ❤ by GitHub

Now I can use the current_theme_supports function in my plugin/theme to add functionality that is supported, like this:

	<?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!';
	}

view raw update-current-theme-supports.php hosted with ❤ by GitHub

And there you have it! You’ve easily extended this core function to further your theme development powers.

Expanding The require_if_theme_supports Function

Another great function related to theme features is the require_if_theme_supports function. Justin Tadlock has a great write up on theme supported features that touches on this function.

Basically, it allows you to conditionally require another file – if theme supports X, include file Y. What if you want to use this function with our example above? Well, you can, but you can’t pass our new sub-features through it. What if you only want to include a file if the custom-footer-text is supported? I’ve written another function you can use in a similar manner. Instead of the main feature, use the sub feature.

	<?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' );