在Users (wp-admin/users.php) 页面，WordPress使用wp_dropdown_users() 要生成您所指的用户下拉菜单，我建议使用wp_dropdown_users_args hook 过滤用户查询，例如仅显示1个结果（或10个，但肯定不是55k！）然后使用JavaScript添加/加载其他结果。

在这个答案中，我将向你展示如何做到这一点，我们在哪里使用Select2 添加“键入并搜索”功能。请注意，我使用的是一个自定义REST API端点，它以Select2所期望的格式返回结果，这样，JavaScript部分/代码对我们来说也会更简单（即代码更短）。

Step #1: Filter the users query for the reassign_user drop-down menu.

function my_filter_reassign_user_query( $query_args, $parsed_args ) {
    // Make sure we\'re on the users.php page on the admin side.
    if ( is_admin() && \'users\' === get_current_screen()->id          &&
        // .. and the action is deleting a user
        ( isset( $_GET[\'action\'] ) && \'delete\' === $_GET[\'action\'] ) &&
        // .. and the <select>\'s name is set to reassign_user.
        \'reassign_user\' === $parsed_args[\'name\']
    ) {
        // You can also use 10, etc., but the point is, we don\'t want 55k (or
        // LOTS OF) <option> tags!
        $query_args[\'number\'] = 1;
    }

    return $query_args;
}
add_filter( \'wp_dropdown_users_args\', \'my_filter_reassign_user_query\', 10, 2 );

Step #2: Enqueue the Select2 scripts and styles, and our AJAX script.

function my_enqueue_select2_scripts() {
    // Make sure we\'re on the users.php page on the admin side.
    if ( is_admin() && \'users\' === get_current_screen()->id ) {
        wp_enqueue_style( \'select2\', \'https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.12/css/select2.min.css\', [], null );
        wp_enqueue_script( \'select2\', \'https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.12/js/select2.full.min.js\', [], null );

        wp_enqueue_script( \'users-ajax\', \'/path/to/users-ajax.js\', [ \'select2\', \'jquery\' ], \'1.0\' );
        wp_localize_script( \'users-ajax\', \'users_ajax\', [
            \'root\'  => esc_url_raw( get_rest_url() ),
            \'nonce\' => wp_create_nonce( \'wp_rest\' ),
        ] );
    }
}
add_action( \'admin_enqueue_scripts\', \'my_enqueue_select2_scripts\' );

Step #3: Register the custom REST API endpoint.

我只是给你密码，看看官方handbook 如果你没有。你还想检查一下WP_User_Query::prepare_query() 对于可以使用的参数。

function my_select2_users( $request ) {
    $search   = $request->get_param( \'term\' );     // the search keyword
    $per_page = $request->get_param( \'per_page\' ); // results per page
    $page     = $request->get_param( \'page\' );     // current page number

    $per_page = $per_page ? $per_page : 10;
    $page     = $page     ? $page     : 1;
    $args     = [
        \'number\'         => $per_page,
        \'paged\'          => $page,
        \'search_columns\' => [ \'user_login\', \'display_name\' ],
        \'fields\'         => [ \'ID\', \'display_name\', \'user_login\' ],
        \'who\'            => \'authors\',
    ];

    if ( $search ) {
        $args[\'search\'] = \'*\' . sanitize_text_field( $search ) . \'*\';
    }

    $query = new WP_User_Query( $args );

    $items = [];
    foreach ( $query->get_results() as $user ) {
        $items[] = [
            \'id\'   => $user->ID,
            \'text\' => $user->display_name . \' (\' . $user->user_login . \')\',
        ];
    }

    return [
        \'results\'    => $items,
        \'pagination\' => [ \'more\' => $page * $per_page < $query->get_total() ],
        \'total\'      => $query->get_total(),
    ];
}

add_action( \'rest_api_init\', function () {
    // You should rename the my-plugin to a meaningful one..
    register_rest_route( \'my-plugin/v1\', \'/select2_users\', [
        \'methods\'             => \'GET\',
        \'callback\'            => \'my_select2_users\',
        \'permission_callback\' => function () {
            return current_user_can( \'delete_users\' );
        }
    ] );
} );

Step #4: The JavaScript/AJAX script (placed in users-ajax.js).

检查here 选择2的参数（如ajax) 您可以使用。

jQuery( function ( $ ) {
    $( \'select[name="reassign_user"]\' ).on( \'select2:open\', function () {
        $( \'#delete_option1\' ).prop( \'checked\', true );
    } ).on( \'select2:select\', function( e ) {
        $( \'#submit\' ).removeProp( \'disabled\' );
    } ).on( \'select2:unselect\', function( e ) {
        $( \'#submit\' ).prop( \'disabled\', true );
    } ).select2( {
        ajax: {
            url: users_ajax.root + \'my-plugin/v1/select2_users\',
            dataType: \'json\',
            headers: { \'X-WP-NONCE\': users_ajax.nonce }
        },
        minimumInputLength: 2
    } );
} );

当所有代码组合在一起时，您会得到如下结果：