add_filter('wp_title') doesn't replace my title tag (WordPress plugin)

user_4189000 0
Viewed 14734

I am trying to change the title of my detail page to the name of the car. I have made a plugin that fills the detail page with the car information. But now I can't get the add_filter('wp_title') to work in my plugin.

Here is the code I tried:

function init() {
    hooks();
}
add_action('wp', 'init');

function hooks() {
    if(get_query_var('car_id') != "") {
        add_filter('wp_title', 'addTitle', 100);
        add_action('wp_head', 'fillHead');
    }
    add_shortcode('showCar', 'showCar');
}

function addTitle() {
    $api_url_klant = API_URL . '/gettitle/' . get_option("ac") . '/' . get_query_var('car_id');
    $title = getJSON($api_url_klant);
    return $title['merk'] . " " . $title['model'] . " - " . $title['bedrijf'];
}

The addTitle() function works just fine. It returns the right name. Also the add_action('wp_head') works as well. I only can't get the wp_title filter not to work.

Am I executing this filter at the wrong moment or what am I doing wrong?

wordpress title plugins
4 Answers

I posted this answer to another question but since it is relevant and more up-to-date, I though it might be useful.

How document title is generated has changed since Wordpress v4.4.0. Now wp_get_document_title dictates how title is generated:

/**
 * Displays title tag with content.
 *
 * @ignore
 * @since 4.1.0
 * @since 4.4.0 Improved title output replaced `wp_title()`.
 * @access private
 */
function _wp_render_title_tag() {
    if ( ! current_theme_supports( 'title-tag' ) ) {
        return;
    }

    echo '<title>' . wp_get_document_title() . '</title>' . "\n";
}

Here is the code from v5.4.2. Here are the filters you can use to manipulate title tag:

function wp_get_document_title() {
    /**
    * Filters the document title before it is generated.
    *
    * Passing a non-empty value will short-circuit wp_get_document_title(),
    * returning that value instead.
    *
    * @since 4.4.0
    *
    * @param string $title The document title. Default empty string.
    */
    $title = apply_filters( 'pre_get_document_title', '' );
    if ( ! empty( $title ) ) {
        return $title;
    }
    // --- snipped ---
    /**
    * Filters the separator for the document title.
    *
    * @since 4.4.0
    *
    * @param string $sep Document title separator. Default '-'.
    */
    $sep = apply_filters( 'document_title_separator', '-' );

    /**
    * Filters the parts of the document title.
    *
    * @since 4.4.0
    *
    * @param array $title {
    *     The document title parts.
    *
    *     @type string $title   Title of the viewed page.
    *     @type string $page    Optional. Page number if paginated.
    *     @type string $tagline Optional. Site description when on home page.
    *     @type string $site    Optional. Site title when not on home page.
    * }
    */
    $title = apply_filters( 'document_title_parts', $title );
    // --- snipped ---
    return $title;
}

So here are two ways you can do it.

First one uses pre_get_document_title filter which short-circuits the title generation and hence more performant if you are not going make changes on current title:

function custom_document_title( $title ) {
    return 'Here is the new title';
}
add_filter( 'pre_get_document_title', 'custom_document_title', 10 );

Second way uses document_title_separator and document_title_parts hooks for the title and the title seperator that are executed later in the function, after title is generated using functions like single_term_title or post_type_archive_title depending on the page and about to be outputted: 

// Custom function should return a string
function custom_seperator( $sep ) {
   return '>';
}
add_filter( 'document_title_separator', 'custom_seperator', 10 );

// Custom function should return an array
function custom_html_title( $title ) {
   return array(
     'title' => 'Custom Title',
     'site'  => 'Custom Site'
    );
}
add_filter( 'document_title_parts', 'custom_html_title', 10 );
user_71341340

I have trawled through each and every solution on the web trying 100s of examples.

In the end... Well Done joemaller As putting this first solved everything!

add_filter('wpseo_title', '__return_empty_string');
user_7946890
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