Useful WordPress Functions

Hide WordPress Update Nag to All But Admins

/**
 * Hide WordPress update nag to all but admins
 */

function hide_update_notice_to_all_but_admin() {
    if ( !current_user_can( 'update_core' ) ) {
        remove_action( 'admin_notices', 'update_nag', 3 );
    }
}
add_action( 'admin_head', 'hide_update_notice_to_all_but_admin', 1 );

Utilize Proper WordPress Titles

Make sure to remove the <title> tag from your header.

/**
 * Utilize proper WordPress titles
 */

add_theme_support( 'title-tag' );

Create Custom WordPress Dashboard Widget

/**
 * Create custom WordPress dashboard widget
 */

function dashboard_widget_function() {
    echo '
        <h2>Custom Dashboard Widget</h2>
        <p>Custom content here</p>
    ';
}

function add_dashboard_widgets() {
    wp_add_dashboard_widget( 'custom_dashboard_widget', 'Custom Dashoard Widget', 'dashboard_widget_function' );
}
add_action( 'wp_dashboard_setup', 'add_dashboard_widgets' );

Remove All Dashboard Widgets

/**
 * Remove all dashboard widgets
 */

function remove_dashboard_widgets() {
    global $wp_meta_boxes;

    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_quick_press'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_incoming_links'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_right_now'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_plugins'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_recent_drafts'] );
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_recent_comments'] );
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_primary'] );
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_secondary'] );

    remove_meta_box( 'dashboard_activity', 'dashboard', 'normal' );
}
add_action( 'wp_dashboard_setup', 'remove_dashboard_widgets' );

Include Navigation Menus

/**
 * Include navigation menus
 */

function register_my_menu() {
    register_nav_menu( 'nav-menu', __( 'Navigation Menu' ) );
}
add_action( 'init', 'register_my_menu' );

Insert this where you want it to appear, and save the menu in Appearance -> Menus.

wp_nav_menu( array( 'theme_location' => 'nav-menu' ) );

Here's the code for multiple menus:

function register_my_menus() {
    register_nav_menus(
        array(
            'new-menu' => __( 'New Menu' ),
            'another-menu' => __( 'Another Menu' ),
            'an-extra-menu' => __( 'An Extra Menu' ),
        )
    );
}
add_action( 'init', 'register_my_menus' );

Insert Custom Login Logo

/**
 * Insert custom login logo
 */

function custom_login_logo() {
    echo '
        <style>
            .login h1 a {
                background-image: url(image.jpg) !important;
                background-size: 234px 67px;
                width:234px;
                height:67px;
                display:block;
            }
        </style>
    ';
}
add_action( 'login_head', 'custom_login_logo' );

Modify Admin Footer Text

/**
 * Modify admin footer text
 */

function modify_footer() {
    echo 'Created by <a href="mailto:you@example.com">you</a>.';
}
add_filter( 'admin_footer_text', 'modify_footer' );

Enqueue Styles and Scripts

/**
 * Enqueue styles and scripts
 */

function custom_scripts() {
    wp_enqueue_style( 'bootstrap', get_template_directory_uri() . '/css/bootstrap.min.css', array(), '3.3.6' );
    wp_enqueue_style( 'style', get_template_directory_uri() . '/css/style.css' );
    wp_enqueue_script( 'bootstrap', get_template_directory_uri() . '/js/bootstrap.min.js', array('jquery'), '3.3.6', true );
    wp_enqueue_script( 'script', get_template_directory_uri() . '/js/script.js' );
}
add_action( 'wp_enqueue_scripts', 'custom_scripts' );

Enqueue Google Fonts

/**
 * Enqueue Google Fonts
 */

function google_fonts() {
    wp_register_style( 'OpenSans', '//fonts.googleapis.com/css?family=Open+Sans:400,600,700,800' );
    wp_enqueue_style( 'OpenSans' );
}
add_action( 'wp_print_styles', 'google_fonts' );

Modify Excerpt Length

/**
 * Modify excerpt length
 */

function custom_excerpt_length( $length ) {
    return 25;
}
add_filter( 'excerpt_length', 'custom_excerpt_length', 999 );

Change Read More Link

/**
 * Change Read More link
 */

function custom_read_more_link() {
    return '<a href="' . get_permalink() . '">Read More</a>';
}
add_filter( 'the_content_more_link', 'custom_read_more_link' );

Change More Excerpt

/**
 * Change More excerpt
 */

function custom_more_excerpt( $more ) {
    return '...';
}
add_filter( 'excerpt_more', 'custom_more_excerpt' );

Disable Emoji Mess

/**
 * Disable Emoji mess
 */

function disable_wp_emojicons() {
    remove_action( 'admin_print_styles', 'print_emoji_styles' );
    remove_action( 'wp_head', 'print_emoji_detection_script', 7 );
    remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
    remove_action( 'wp_print_styles', 'print_emoji_styles' );
    remove_filter( 'wp_mail', 'wp_staticize_emoji_for_email' );
    remove_filter( 'the_content_feed', 'wp_staticize_emoji' );
    remove_filter( 'comment_text_rss', 'wp_staticize_emoji' );
    add_filter( 'tiny_mce_plugins', 'disable_emojicons_tinymce' );
    add_filter( 'emoji_svg_url', '__return_false' );
}
add_action( 'init', 'disable_wp_emojicons' );

function disable_emojicons_tinymce( $plugins ) {
    return is_array( $plugins ) ? array_diff( $plugins, array( 'wpemoji' ) ) : array();
}

Remove Comments

/**
 * Remove comments
 */

// Removes from admin menu

function my_remove_admin_menus() {
    remove_menu_page( 'edit-comments.php' );
}
add_action( 'admin_menu', 'my_remove_admin_menus' );

// Removes from post and pages
function remove_comment_support() {
    remove_post_type_support( 'post', 'comments' );
    remove_post_type_support( 'page', 'comments' );
}
add_action( 'init', 'remove_comment_support', 100 );

// Removes from admin bar
function mytheme_admin_bar_render() {
    global $wp_admin_bar;

    $wp_admin_bar->remove_menu( 'comments' );
}
add_action( 'wp_before_admin_bar_render', 'mytheme_admin_bar_render' );

Change Media Gallery URL

/**
 * Change Media Gallery URL
 */

if ( empty( get_option( 'upload_url_path' ) ) ) {
    update_option( 'upload_url_path', 'http://assets.website.com/wp-content/uploads' );
}

Also, you can filter the option value before it's retrieved from the database, which is slightly better:

/**
 * Change Media Gallery URL
 */

add_filter( 'pre_option_upload_url_path', function() {
    return 'http://assets.website.com/wp-content/uploads';
});

Create Custom Thumbnail Size

/**
 * Create custom thumbnail size
 */

add_image_size( 'custom-thumbnail', 250, 250, true );

Retrieve Thumbnail

$thumb = wp_get_attachment_image_src( get_post_thumbnail_id($post->ID), 'custom-thumbnail' );

echo $thumb[0];

Since WordPress 4.4.0, you can use:

the_post_thumbnail_url( $size );

Add Categories for Attachments

/**
 * Add categories for attachments
 */

function add_categories_for_attachments() {
    register_taxonomy_for_object_type( 'category', 'attachment' );
}
add_action( 'init' , 'add_categories_for_attachments' );

Add Tags for Attachments

/**
 * Add tags for attachments
 */

function add_tags_for_attachments() {
    register_taxonomy_for_object_type( 'post_tag', 'attachment' );
}
add_action( 'init' , 'add_tags_for_attachments' );

Add Custom Excerpt to Pages

/**
 * Add custom excerpt to pages
 */

function add_page_excerpt() {
    add_post_type_support( 'page', array( 'excerpt' ) );
}
add_action( 'init', 'add_page_excerpt' );

Create a Global String

/**
 * Create a global string
 */

function global_string() {
    return 'String';
}

Retrieve Field

echo global_string();

Support Featured Images

/**
 * Support featured images
 */

add_theme_support( 'post-thumbnails' );

Support Search Form

/**
 * Support search form
 */

add_theme_support( 'html5', array( 'search-form' ) );

Excluding Pages From Search

/**
 * Excluding pages from search
 */

function exclude_pages_from_search() {
    global $wp_post_types;

    $wp_post_types['page']->exclude_from_search = true;
}
add_action( 'init', 'exclude_pages_from_search' );

Disable xmlrpc.php

/**
 * Disable xmlrpc.php
 */

add_filter( 'xmlrpc_enabled', '__return_false' );
remove_action( 'wp_head', 'rsd_link' );
remove_action( 'wp_head', 'wlwmanifest_link' );

Escape HTML in Posts

/**
 * Escape HTML in <code> or <pre><code> tags.
 */

function escapeHTML($arr) {
    if (version_compare(PHP_VERSION, '5.2.3') >= 0) {
        $output = htmlspecialchars($arr[2], ENT_NOQUOTES, get_bloginfo('charset'), false);
    }
    else {
        $specialChars = array(
            '&' => '&amp;',
            '<' => '&lt;',
            '>' => '&gt;'
        );

        // decode already converted data
        $data = htmlspecialchars_decode( $arr[2] );
        // escape all data inside <pre>
        $output = strtr( $data, $specialChars );
    }
    if (! empty($output)) {
        return  $arr[1] . $output . $arr[3];
    }    else     {
        return  $arr[1] . $arr[2] . $arr[3];
    }
}
function filterCode($data) { // Uncomment if you want to escape anything within a <pre> tag
    //$modifiedData = preg_replace_callback( '@(<pre.*>)(.*)(<\/pre>)@isU', 'escapeHTML', $data );
    $modifiedData = preg_replace_callback( '@(<code.*>)(.*)(<\/code>)@isU', 'escapeHTML', $data );
    $modifiedData = preg_replace_callback( '@(<tt.*>)(.*)(<\/tt>)@isU', 'escapeHTML', $modifiedData );

    return $modifiedData;
}
add_filter( 'content_save_pre', 'filterCode', 9 );
add_filter( 'excerpt_save_pre', 'filterCode', 9 );

Modified from Escape HTML.

Create Custom Global Settings

/**
 * Create custom global settings
 */

function custom_settings_page() { ?>
    <div class="wrap">
    <h1>Custom Settings</h1>
    <form method="post" action="options.php">
        <?php
            settings_fields( 'section' );
            do_settings_sections( 'theme-options' );
            submit_button();
        ?>
    </form>
    </div>
<?php }

function custom_settings_add_menu() {
    add_theme_page( 'Custom Settings', 'Custom Settings', 'manage_options', 'custom-settings', 'custom_settings_page', null, 99 );
}
add_action( 'admin_menu', 'custom_settings_add_menu' );

// Example setting
function setting_twitter() { ?>
    <input type="text" name="twitter" id="twitter" value="<?php echo get_option('twitter'); ?>" />
<?php }

function custom_settings_page_setup() {
    add_settings_section( 'section', 'All Settings', null, 'theme-options' );
    add_settings_field( 'twitter', 'Twitter Username', 'setting_twitter', 'theme-options', 'section' );
    register_setting( 'section', 'twitter' );
}
add_action( 'admin_init', 'custom_settings_page_setup' );

Retrieve Field

echo get_option( 'twitter' );

Modified from Create a WordPress Theme Settings Page with the Settings API.

Remove WordPress Admin Bar

/**
 * Remove WordPress admin bar
 */

function remove_admin_bar() {
    remove_action( 'wp_head', '_admin_bar_bump_cb' );
}
add_action( 'get_header', 'remove_admin_bar' );

Add Open Graph Meta Tags

/**
 * Add Open Graph Meta Tags
 */

function meta_og() {
    global $post;

    if ( is_single() ) {
        if( has_post_thumbnail( $post->ID ) ) {
            $img_src = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'thumbnail' );
        }
        $excerpt = strip_tags( $post->post_content );
        $excerpt_more = '';
        if ( strlen($excerpt ) > 155) {
            $excerpt = substr( $excerpt,0,155 );
            $excerpt_more = ' ...';
        }
        $excerpt = str_replace( '"', '', $excerpt );
        $excerpt = str_replace( "'", '', $excerpt );
        $excerptwords = preg_split( '/[\n\r\t ]+/', $excerpt, -1, PREG_SPLIT_NO_EMPTY );
        array_pop( $excerptwords );
        $excerpt = implode( ' ', $excerptwords ) . $excerpt_more;
        ?>
<meta name="author" content="Your Name">
<meta name="description" content="<?php echo $excerpt; ?>">
<meta property="og:title" content="<?php echo the_title(); ?>">
<meta property="og:description" content="<?php echo $excerpt; ?>">
<meta property="og:type" content="article">
<meta property="og:url" content="<?php echo the_permalink(); ?>">
<meta property="og:site_name" content="Your Site Name">
<meta property="og:image" content="<?php echo $img_src[0]; ?>">
<?php
    } else {
        return;
    }
}
add_action('wp_head', 'meta_og', 5);

Add Custom Post Type

/**
 * Add custom post type
 */

function create_custom_post() {
    register_post_type( 'custom-post', // slug for custom post type
        array(
        'labels' => array(
            'name' => __( 'Custom Post' ),
        ),
        'public' => true,
        'hierarchical' => true,
        'has_archive' => true,
        'supports' => array(
            'title',
            'editor',
            'excerpt',
            'thumbnail'
        ),
        'can_export' => true,
        'taxonomies' => array(
                'post_tag',
                'category'
        )
    ));
}
add_action('init', 'create_custom_post');

Implement Preconnect to Google Fonts in Themes

/**
 * Implement preconnect to Google Fonts in themes
 */

function twentyfifteen_resource_hints( $urls, $relation_type ) {
    // Checks whether the subject is carrying the source of fonts google and the `$relation_type` equals preconnect.
    // Replace `enqueue_font_id` the `ID` used in loading the source.
    if ( wp_style_is( 'enqueue_font_id', 'queue' ) && 'preconnect' === $relation_type ) {
        // Checks whether the version of WordPress is greater than or equal to 4.7
        // to ensure compatibility with older versions
        // because the 4.7 has become necessary to return an array instead of string
        if ( version_compare( $GLOBALS['wp_version'], '4.7-alpha', '>=' ) ) {
            // Array with url google fonts and crossorigin
            $urls[] = array(
                'href' => 'https://fonts.gstatic.com',
                'crossorigin',
            );
        } else {
            // String with url google fonts
            $urls[] = 'https://fonts.gstatic.com';
        }
    }
    return $urls;
}
add_filter( 'wp_resource_hints', 'twentyfifteen_resource_hints', 10, 2 );

Add Thumbnail Column to Post Listing

/**
 * Add thumbnail column to post listing
 */

add_image_size( 'admin-list-thumb', 80, 80, false );

function wpcs_add_thumbnail_columns( $columns ) {

    if ( !is_array( $columns ) )
        $columns = array();
    $new = array();

    foreach( $columns as $key => $title ) {
        if ( $key == 'title' ) // Put the Thumbnail column before the Title column
            $new['featured_thumb'] = __( 'Image');
        $new[$key] = $title;
    }
    return $new;
}

function wpcs_add_thumbnail_columns_data( $column, $post_id ) {
    switch ( $column ) {
    case 'featured_thumb':
        echo '<a href="' . $post_id . '">';
        echo the_post_thumbnail( 'admin-list-thumb' );
        echo '</a>';
        break;
    }
}

if ( function_exists( 'add_theme_support' ) ) {
    add_filter( 'manage_posts_columns' , 'wpcs_add_thumbnail_columns' );
    add_action( 'manage_posts_custom_column' , 'wpcs_add_thumbnail_columns_data', 10, 2 );
}

Add Lead Class to First Paragraph

/**
 * Add lead class to first paragraph
 */

function first_paragraph( $content ) {
    return preg_replace( '/<p([^>]+)?>/', '<p$1 class="lead">', $content, 1 );
}
add_filter( 'the_content', 'first_paragraph' );

Adds a lead class to the first paragraph in the_content.

Exclude Custom Post Type from Search

/**
 * Exclude custom post type from search
 */

function excludePages( $query ) {
if ( $query->is_search ) {
    $query->set( 'post_type', 'post' );
}
    return $query;
}
add_filter( 'pre_get_posts','excludePages' );

Remove Query String from Static Resources

/**
 * Remove query string from static resources
 */

function remove_cssjs_ver( $src ) {
    if ( strpos( $src, '?ver=' ) )
        $src = remove_query_arg( 'ver', $src );
    return $src;
}
add_filter( 'style_loader_src', 'remove_cssjs_ver', 10, 2 );
add_filter( 'script_loader_src', 'remove_cssjs_ver', 10, 2 );

Modify jQuery

/**
 * Modify jQuery
 */

function modify_jquery() {
    wp_deregister_script( 'jquery' );
    wp_register_script( 'jquery', 'https://ajax.googleapis.com/ajax/libs/jquery/3.2.1/jquery.min.js', false, '3.2.1' );
    wp_enqueue_script( 'jquery' );
}
if (!is_admin()) add_action('wp_enqueue_scripts', 'modify_jquery');

Disable Website Field From Comment Form

/**
 * Disable website field from comment form
 */

function disable_website_field( $field ) {
    if( isset($field['url']) ) {
        unset( $field['url'] );
    }
    return $field;
}
add_filter('comment_form_default_fields', 'disable_website_field');

Disable JSON REST API

/**
 * Disable JSON REST API
 */

add_filter('json_enabled', '__return_false');
add_filter('json_jsonp_enabled', '__return_false');

Switch Post Type

/**
 * Switch post type
 */

function switch_post_type ( $old_post_type, $new_post_type ) {
    global $wpdb;

    // Run the update query
    $wpdb->update(
        $wpdb->posts,
        // Set
        array( 'post_type' => $new_post_type),
        // Where
        array( 'post_type' => $old_post_type )
    );
}

PHP Logger

/**
 * PHP Logger
 */

function php_logger( $data ) {
    $output = $data;
    if ( is_array( $output ) )
        $output = implode( ',', $output );

    // print the result into the JavaScript console
    echo "<script>console.log( 'PHP LOG: " . $output . "' );</script>";
}

Always Show Second Bar in TinyMCE

/**
 * Always show second bar in TinyMCE
 */

function show_tinymce_toolbar( $in ) {
    $in['wordpress_adv_hidden'] = false;
    return $in;
}
add_filter( 'tiny_mce_before_init', 'show_tinymce_toolbar' );

Remove Admin Menu Items Depending on User Role

/**
 * Clone the administrator user role
 */

function clone_admin_role() {
    global $wp_roles;
    if ( ! isset( $wp_roles ) )
        $wp_roles = new WP_Roles();

    $adm = $wp_roles->get_role( 'administrator' );

    // Add new "Client" role with all admin capabilities
    $wp_roles->add_role( 'client', 'Client', $adm->capabilities );
}
add_action( 'init', 'clone_admin_role' );

/**
 * Specify which admin menu items are visible for users with role "Client"
 */

function remove_dashboard_menus() {
    if ( current_user_can( 'client' ) ) {
        // Hide Updates under Dashboard menu
        remove_submenu_page( 'index.php', 'update-core.php' );

        // Hide Comments
        remove_menu_page( 'edit-comments.php' );

        // Hide Plugins
        remove_menu_page( 'plugins.php' );

        // Hide Themes, Customizer and Widgets under Appearance menu
        remove_submenu_page( 'themes.php', 'themes.php' );
        remove_submenu_page( 'themes.php', 'customize.php?return=' . urlencode( $_SERVER['REQUEST_URI'] ) );
        remove_submenu_page( 'themes.php', 'widgets.php' );

        // Hide Tools
        remove_menu_page( 'tools.php' );

        // Hide General Settings
        remove_menu_page( 'options-general.php' );
    }
}
add_action( 'admin_menu', 'remove_dashboard_menus' );

Remove Admin Menu Items Depending on Email Address (domain)

/**
 * Specify which users can see admin menu items based on their email address
 */

function remove_dashboard_menus() {
    $user_data = get_userdata( get_current_user_id() );
    $user_email = isset( $user_data->user_email ) ? $user_data->user_email : '';

    if ( ! strpos( $user_email, '@yourcompany.com' ) ) {
        // Hide Updates under Dashboard menu
        remove_submenu_page( 'index.php', 'update-core.php' );

        // Hide Comments
        remove_menu_page( 'edit-comments.php' );

        // Hide Plugins
        remove_menu_page( 'plugins.php' );

        // Hide Themes, Customizer and Widgets under Appearance menu
        remove_submenu_page( 'themes.php', 'themes.php' );
        remove_submenu_page( 'themes.php', 'customize.php?return=' . urlencode( $_SERVER['REQUEST_URI'] ) );
        remove_submenu_page( 'themes.php', 'widgets.php' );

        // Hide Tools
        remove_menu_page( 'tools.php' );

        // Hide General Settings
        remove_menu_page( 'options-general.php' );
    }
}
add_action( 'admin_menu', 'remove_dashboard_menus' );

Reorder Admin Menu Items

/**
 * Reorder admin menu
 */

function custom_menu_order( $menu_ord ) {
    if ( ! $menu_ord ) { return true; }
        return array(
            'index.php',
            'separator1',
            'edit.php?post_type=page',
            'edit.php',
            'edit.php?post_type=[your_post_type_slug]',
            'upload.php',
            'edit-comments.php',
            'separator2',
            'themes.php',
            'plugins.php',
            'users.php',
            'tools.php',
            'options-general.php'
        );
    }
}
add_filter( 'custom_menu_order', 'custom_menu_order' );
add_filter( 'menu_order', 'custom_menu_order' );

Exclude a Category From WordPress Loops

/**
 * Exclude a category from all WordPress loops
 */

add_action( 'pre_get_posts', function( $query ) { // anonymous callback

    global $wp_query;

    // Hard coded category ID, but can be dynamic: esc_attr(get_option('your-cat-id'));
    $excluded_cat_id = 25;

    // add category ID to existing, avoid overwriting it
    $cat[] = $query->get( 'cat' );
    $cat[] = "-" . $excluded_cat_id;

    $query->set( 'cat', $cat );
    }
});

Disable the message - JQMIGRATE: Migrate is installed, version 1.4.1

add_action('wp_default_scripts', function ($scripts) {
    if (!empty($scripts->registered['jquery'])) {
        $scripts->registered['jquery']->deps = array_diff($scripts->registered['jquery']->deps, ['jquery-migrate']);
    }
});

Load heavy 3rd-party scripts later for better performance

Lighthouse and similar performance analysis tools always complain about render-blocking scripts (and styles), short cache TTL etc. Most of these scripts and styles come from 3rd-party sources which we can't control – Google's own Tag Manager and Analytics, Facebook Pixel, other trackers and chat scripts etc. However, we can load them only when a real user interacts with a page, significantly reducing the Time To Interactive metric and scoring much higher performance results.

Depending on where you like these 3rd-party scripts to be, you can either use wp_footer action to print the code in footer, or put it in your main app.js script which, in turn, is enqueued on wp_enqueue_scripts action.

<script>
var fired = false;

window.addEventListener('scroll', () => {
    if (fired === false) {
        fired = true;

        setTimeout(() => {

            // Marketing scripts go here.

        }, 1000) // 1000ms or 1s works fine, but you can adjust this timeout.
    }
});
</script>