这是一个用于回答问题的示例插件，前端使用ajaxurl。

so-random-quotes.php

 plugin_dir_path( __FILE__ ).'quotes.txt',
        ), $atts );
        // shortcode replacement
        $out = sprintf(
                    '%sNew Quote',
                    self::DOM_TARGET,
                    $this->getQuote($got['path'])
               );
        // loading js
        // jquery depends
        wp_enqueue_script('sorandquo-js', plugin_dir_url( __FILE__ ).'quote-loader.js', array('jquery'));
        // passing to js needed vars
        wp_localize_script( 'sorandquo-js', 'ajaxParams',
            array(
                'path'      => $got['path'], // path to qoutes file
                'targetDom' => '#'.self::DOM_TARGET, // dom path to put resulting qoute
                'ajaxurl'   => admin_url( 'admin-ajax.php'), // for frontend ( not admin )
                'action'    => self::AJAX_ACTION, //
            )
        );
        // render shortcode replacement
        return $out;
    }
    /**
     * Ajax Callback
     */
    public function getQuoteAjax(){
        echo $this->getQuote($_POST['path']);
        die();
    }
    /**
     * Getting random Qoute from the file
     * @param $path
     * @return mixed
     */
    public function getQuote($path){
        $quotesFile = is_file($path) ? file_get_contents($path):"File {$path} not found";
        $quotesArr = $quotesFile ? explode("\n", $quotesFile):['Quotes File is empty'];
        return $quotesArr[array_rand($quotesArr)];
    }
}

quote-loader.js

jQuery.noConflict();
jQuery(document).ready(function($) {
    $(document).on('click', '#newquote', function (e) {
        e.preventDefault();
        $.post(ajaxParams.ajaxurl, {
            'action':ajaxParams.action,
            'path'  :ajaxParams.path
        }, function (ret) {
            $(ajaxParams.targetDom).html(ret);
        }, 'html');
    });
});

很好的问题！

但是，由于您的代码以不良习惯开始——require_once('wp-load.php');——我决定选择我的一个工作片段并进行适应。

观察：

• 与您的代码不同，没有抓取外部quotes.txt文件，这里使用文章类型作为源（post），在方法get_random_post中
• 在给定页面中只能有一个实例的短代码，因为它基于特定的元素ID（#newpost-shortcode和#randomposts）
• 通常，最好为此创建一个插件。请遵循代码注释。

/wp-content/plugins/so-ajax-shortcode/so-ajax-shortcode.php

plugin_url = plugins_url( '/', __FILE__ );
        add_shortcode( 'randomposts', array( $this, 'shortcode') );
        add_action( 'wp_enqueue_scripts', array( $this, 'enqueue' ) );
        add_action( 'wp_ajax_query_rand_post', array( $this, 'query_rand_post' ) );
        add_action( 'wp_ajax_nopriv_query_rand_post', array( $this, 'query_rand_post' ) );
    }
    /**
     * SHORTCODE output
     */
    public function shortcode( $atts ) 
    {
        # First post
        if( ! $random_post = $this->get_random_post() )
            $random_post = __( 'Could not retrieve a post.' );
        # Prepare output
        $output = sprintf(
            '%s
             %s',
            $random_post,
            __( 'Gimme a new one!' ),
            __( 'New random post' )
        );
        return $output;
    }
    /**
     * ACTION Enqueue scripts
     */
    public function enqueue() 
    {
        # jQuery will be loaded as a dependency
        ## DO NOT use other version than the one bundled with WP
        ### Things will BREAK if you do so
        wp_enqueue_script( 
             'ajax-random-post',
             "{$this->plugin_url}ajax.js",
             array( 'jquery' )
        );
        # Here we send PHP values to JS
        wp_localize_script( 
             'ajax-random-post',
             'wp_ajax',
             array( 
                 'ajaxurl'      => admin_url( 'admin-ajax.php' ),
                 'ajaxnonce'   => wp_create_nonce( 'ajax_post_validation' ),
                 'loading'    => 'http://i.stack.imgur.com/drgpu.gif'
            ) 
        );
    }
    /**
     * AJAX query random post
     * 
     * Check for security and send proper responses back
     */
    public function query_rand_post()
    {
        check_ajax_referer( 'ajax_post_validation', 'security' );
        $random_post = $this->get_random_post();
        if( !isset( $random_post ) )
            wp_send_json_error( array( 'error' => __( 'Could not retrieve a post.' ) ) );
        else
            wp_send_json_success( $random_post );
    }
    /**
     * AUX FUNCTION 
     * Search a random Post Type and return the post_content
     */
    public function get_random_post()
    {
        $array = get_posts( 
            array( 
                  'post_type' => $this->cpt,
                  'numberposts' => -1 
            ) 
        );
        if( empty( $array ) )
            return false;
        # Select a random post index number from the current array
        $r = rand( 0, count($array) - 1 );
        return $array[$r]->post_content;
    }
}

/wp-content/plugins/so-ajax-shortcode/ajax.js

/* 
 * @plugin SO Ajax Shortcode
 */
jQuery( document ).ready( function( $ ) 
{ 
     var data = {
         action: 'query_rand_post',
         security: wp_ajax.ajaxnonce
     };
     var image = '';
    $( '#newpost-shortcode' ).click( function(e) 
    {
        e.preventDefault();
        $( '#randomposts' ).html( image );
        $.post( 
            wp_ajax.ajaxurl, 
            data,                   
            function( response )
            {
                // ERROR HANDLING
                if( !response.success )
                {
                    // No data came back, maybe a security error
                    if( !response.data )
                        $( '#randomposts' ).html( 'AJAX ERROR: no response' );
                    else
                        $( '#randomposts' ).html( response.data.error );
                }
                else
                    $( '#randomposts' ).html( response.data );
            }
        ); 
    }); // end click
});