问得好！
但是，由于您的代码以一个不好的实践require_once('wp-load.php');开头，我决定选择一个工作片段并对其进行修改。

*意见：
*与您的代码不同，未获取外部quotes.txt，此处将Post Type用作方法get_random_post中的源（post）
*给定页面中只能有一个短代码示例，因为它基于特定元素ID（#newpost-shortcode和#randomposts）

• 像往常一样，it's better to create a plugin用于此。遵循代码注解。

/wp-内容/插件/so-ajax-短代码/so-ajax-短代码. php

<?php
/**
 * Plugin Name: (SO) Ajax Shortcode
 * Description: Demonstration of WordPress Ajax working as a shortcode.
 * Plugin URI:  http://stackoverflow.com/a/13614297/1287812
 * Version:     2013.10.25
 * Author:      Rodolfo Buaiz
 * Author URI:  https://wordpress.stackexchange.com/users/12615/brasofilo
 * License:     GPLv3
 */

add_action(
    'plugins_loaded',
    array ( B5F_SO_13498959::get_instance(), 'plugin_setup' )
);

class B5F_SO_13498959
{
    private $cpt = 'post'; # Adjust the CPT
    protected static $instance = NULL;
    public $plugin_url = '';
    public function __construct() {}

    public static function get_instance()
    {
        NULL === self::$instance and self::$instance = new self;
        return self::$instance;
    }

    /**
     * Regular plugin work
     */
    public function plugin_setup()
    {
        $this->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(
            '<div id="randomposts">%s</div>
             <button id="newpost-shortcode" type="button" title="%s">%s</button>',
            $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 = '<img src="' + wp_ajax.loading + '" alt="Loading ..." width="16" height="16" />';

    $( '#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
});

这里的例子插件作为问题的答案。使用ajaxurl在前端。

• 随机引用.php*

<?php
/*
Plugin Name: SO Random Quotes
Plugin URI: http://azzrael.ru
Description: Reference to http://stackoverflow.com/questions/13498959/how-to-use-ajax-in-a-wordpress-shortcode
Version: 1.0.0
Author: Azzrael
Author URI: http://azzrael.ru
*/

new SoRandomQuotes();

/**
 * Class SoRandomQuotes
 */
class SoRandomQuotes{

    const SHORTCODE_KEY = 'randomquotes'; // usage [randomquotes path='/path/to/file/another.quotes.csv']
    const AJAX_ACTION = 'so_getnewquote'; // ajax action
    const DOM_TARGET =  'randomquotes'; // dom element to put the quotes

    /**
     * SoRandomQuotes constructor.
     * init actions
     */
    function __construct() {
        // adding shortcode
        add_shortcode('randomquotes', array($this, 'addShortcode'));

        // adding ajax callbacks
        add_action( 'wp_ajax_'.self::AJAX_ACTION, array($this, 'getQuoteAjax')); // admin
        add_action( 'wp_ajax_nopriv_'.self::AJAX_ACTION, array($this, 'getQuoteAjax')); // front
    }

    /**
     * Shortcode callback
     * @param $atts
     * @return string
     */
    public function addShortcode($atts){

        // getting path value from shortcode atts
        $got =shortcode_atts( array(
            'path'    => plugin_dir_path( __FILE__ ).'quotes.txt',
        ), $atts );

        // shortcode replacement
        $out = sprintf(
                    '<div id="%s">%s</div><a id="newquote" class="button" href="#" title="Gimme a new one!">New Quote</a>',
                    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)];
    }

}

• 报价加载程序.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');
    });
});

Wordpress简码和你给予参数的函数一样，
为了创建 AJAX 请求，你可以在你的头文件或函数文件中使用jQuery.ajax或xmlhttp，并带有add_action wp_head钩子。
你应该在你的主题文件夹中创建ajax.php，在文件的顶部你应该包括wp-load.php，并以适当的方式放置你所有的ajax函数。

触发器中使用的选择器与按钮ID不匹配。
将jQuery('#newquotes')更改为jQuery('#newquote')

在function.php中添加这个函数：

<?php
    add_action('wp_head','ajaxurl');
    function ajaxurl()
    {
    ?>
        <script type="text/javascript">
        var ajaxurl = '<?php echo admin_url('admin-ajax.php'); ?>';
        </script>
    <?php
    }?>