Template tags and conditional tags

Two kinds of tags

Classic themes build pages out of PHP functions. There are two groups:

• Template tags print or return data: the site name, a post's title, a menu, a pagination bar.
• Conditional tags return true or false for the request being shown: "is this the front page?", "is this a category archive?". You use them in if statements.

The previous lesson covered the tags used inside the Loop. Here are the ones that work anywhere.

Site information

<?php
echo get_bloginfo( 'name' ), "\n";
echo get_bloginfo( 'description' ), "\n";
echo home_url( '/' ), "\n";
echo site_url( '/wp-login.php' ), "\n";
echo admin_url( 'edit.php' ), "\n";
echo get_bloginfo( 'language' ), "\n";
echo get_bloginfo( 'version' ), "\n";

My WordPress Site

http://localhost:8080/
http://localhost:8080/wp-login.php
http://localhost:8080/wp-admin/edit.php
en-US
7.1.3

bloginfo( 'name' ) prints, get_bloginfo( 'name' ) returns. For addresses, use the URL functions rather than writing a domain by hand: home_url() is the address visitors use, site_url() is where WordPress itself is installed (usually the same), and admin_url() is for the dashboard. In theme files use get_theme_file_uri() for files in your theme.

Conditional tags

/*
Theme Name: Tags Demo
Version: 1.0.0
*/

<?php
$kind = 'something else';
if ( is_front_page() )      { $kind = 'front page'; }
elseif ( is_home() )        { $kind = 'blog page'; }
elseif ( is_single() )      { $kind = 'single post'; }
elseif ( is_page() )        { $kind = 'page'; }
elseif ( is_category() )    { $kind = 'category archive'; }
elseif ( is_search() )      { $kind = 'search results'; }
elseif ( is_404() )         { $kind = 'not found'; }
echo '<p class="kind">', esc_html( $kind ), '</p>';

wp theme activate tags-demo

Success: Switched to 'Tags Demo' theme.

Each address now reports what WordPress thinks it is:

GET /

front page

GET /hello-world/

single post

GET /sample-page/

page

GET /category/uncategorized/

category archive

GET /?s=hello

search results

GET /missing/

not found

The most used conditional tags:

Static front pages and is_home()

The names confuse everyone once. When the site shows latest posts on the front page, is_front_page() and is_home() are both true on /. When you choose a static page as the front page and another page for posts (Settings → Reading), is_front_page() is true on the static page and is_home() is true on the posts page. Test them on a real site before you rely on them.

Reusing pieces of markup

To avoid copying markup between templates, put it in a file and load it with get_template_part():

<article class="card">
	<h2><?php echo esc_html( get_the_title() ); ?></h2>
</article>

<?php
while ( have_posts() ) {
	the_post();
	get_template_part( 'parts/card' );
}

GET /hello-world/

Hello world!

A child theme can replace parts/card.php with its own copy, and you can pass a second argument (get_template_part( 'parts/card', 'wide' ) loads parts/card-wide.php) or a third array of variables, which the file reads as $args.

Navigation tags

For lists of posts, the tags the_posts_pagination() (numbered pages), the_posts_navigation() (older / newer links) and the_post_navigation() (previous / next post on a single page) print navigation with the right links and screen-reader text. Menus use wp_nav_menu(), which you meet in Navigation menus.

Escape what you print

Template tags such as the_title() already return safe, filtered values. Whatever you build yourself must be escaped when you print it: esc_html() for text, esc_attr() for attribute values, esc_url() for addresses. The conditional above does this with esc_html( $kind ).

Common mistakes

• Using is_home() when you mean the front page.
• Using is_single() for pages (use is_page() or is_singular()).
• Calling is_*() tags too early, for example from the init hook, before the query has run. Use wp or later, or the template itself.
• Echoing get_* functions without echo, or echoing the_* functions.

Exercise

Change index.php so that it prints "Welcome back" only to logged-in visitors, on the front page.

<?php
if ( is_front_page() && is_user_logged_in() ) {
	echo '<p>Welcome back, ', esc_html( wp_get_current_user()->display_name ), '</p>';
}