Add "Previous" and "Next" links to the pager

functions.php

<?php

add_filter( 'facetwp_pager_html', function( $output, $params ) {
    $output = '';
    $page = $params['page'];
    $total_pages = $params['total_pages'];

    if ( 1 < $total_pages ) {

        // Previous page (NEW)
        if ( $page > 1 ) {
            $output .= '<a class="facetwp-page" data-page="' . ($page - 1) . '">Previous</a>';
        }
        
        if ( 3 < $page ) {
            $output .= '<a class="facetwp-page first-page" data-page="1">&lt;&lt;</a>';
        }
        if ( 1 < ( $page - 10 ) ) {
            $output .= '<a class="facetwp-page" data-page="' . ($page - 10) . '">' . ($page - 10) . '</a>';
        }
        for ( $i = 2; $i > 0; $i-- ) {
            if ( 0 < ( $page - $i ) ) {
                $output .= '<a class="facetwp-page" data-page="' . ($page - $i) . '">' . ($page - $i) . '</a>';
            }
        }

        // Current page
        $output .= '<a class="facetwp-page active" data-page="' . $page . '">' . $page . '</a>';

        for ( $i = 1; $i <= 2; $i++ ) {
            if ( $total_pages >= ( $page + $i ) ) {
                $output .= '<a class="facetwp-page" data-page="' . ($page + $i) . '">' . ($page + $i) . '</a>';
            }
        }
        if ( $total_pages > ( $page + 10 ) ) {
            $output .= '<a class="facetwp-page" data-page="' . ($page + 10) . '">' . ($page + 10) . '</a>';
        }
        if ( $total_pages > ( $page + 2 ) ) {
            $output .= '<a class="facetwp-page last-page" data-page="' . $total_pages . '">&gt;&gt;</a>';
        }

        // Next page (NEW)
        if ( $page < $total_pages ) {
            $output .= '<a class="facetwp-page" data-page="' . ($page + 1) . '">Next</a>';
        }
    }

    return $output;
}, 10, 2 );