A simple WP plugin to know how AJAX works on WordPress

ajax_example.js

/**
 * @param {string} security_nonce 
 *        Code of the Nonce. Security Stuff
 */

jQuery(function($)
{
    // The call trigered
    $('#publish').click(function(event)
    {
        var day = $('#jj').val();

        event.preventDefault();
        //---------------- ajax call ----------------
        $.ajax(
        {
            url: ajaxurl,
            type: 'POST',
            dataType: 'json',
            data: 
            {
                //the WP actions that is going to receive this 
                action: 'ajax_action_example',
                //security stuff
                security_nonce: security_nonce,
                // Custom data
                day: day
            },
            //timeout: 30000,
            success: function( response ) 
            {
                if(response.success)
                {
                    console.log( 'succ: ', response );
                    $('#publish').unbind('click');
                    $('#publish').trigger('click');
                }
                else
                    console.log( 'fail: ', response );
            },
            // Conection Error
            error: function( error ) 
            {
                console.log( 'Conection error: ', error );
            }
        });
        //---------------- ajax call ----------------        
    });
});

ajax_example.php

<?php
/*
Plugin Name: Ajax Example
Description: A simple WP plugin to know how AJAX works on WordPress
Author: Diego Juliao
Version: 0.1
Author URI: https://about.me/dianjuar
*/

if( !class_exists('ajax_example') )
{
    define( 'AJAXEX_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
    define( 'AJAXEX_PLUGIN_URL', plugin_dir_url( __FILE__ ) );
    define('AJAXEX_PLUGIN_DIRNAME', plugin_basename(dirname(__FILE__)));
    define( 'AJAXEX', 'ajax_example' );

/**
 * A very simple example to demonstrate how AJAX calls works.
 *
 * The logic is, the user can publish a post only the 4th days of every month
 */
class ajax_example
{
    function __construct()
    {
        # Enqueue the JS scripts
        add_action( 'admin_enqueue_scripts',
            array(&$this, 'enqueueScripts'));

        # Ajax listener, teacher crate a payment request
        add_action('wp_ajax_ajax_action_example',
            array(&$this, 'ajax_request_receiver') );
    }
    
    /**
     * Enqueue the JavaScript files
     */
    public function enqueueScripts()
    {
        #---------------WHERE TO PUT THE SCRIPTS ON---------------
        # Here you will specify where you want to enqueue the js file to make the ajax request
        global $current_screen;

        # Only when the user is viewing the owlo_paid_to_teacher screen
        if( $current_screen->post_type !== 'post' )
            return;
        #---------------WHERE TO PUT THE SCRIPTS OFF --------------
        
        wp_enqueue_script( 'ajax_request_script', 
                            AJAXEX_PLUGIN_URL.'ajax_example.js', 
                            array( 'jquery' ), 
                            '0.0', 
                            true );

        # Send the parameters to the script
        # Security stuff.
        $security_nonce = wp_create_nonce( IS_NONCE );
        wp_localize_script( 'ajax_request_script', 
                            'security_nonce', 
                            $security_nonce );
    }

    /**
     * Function to attend the ajax call
     */
    public function ajax_request_receiver()
    {
        # ------------------------- SECURITY VALIDATION ON ----------------------------- 
        /**
         * Checks if the nonce of the ajax is valid
         * 
         * First parameters comes for the wp_nonce_field string
         * and the second one comes for the ajax parameter
         */
        if( !check_ajax_referer(IS_NONCE, 'security_nonce') )
            return wp_send_json_error( 'Invalid Nonce'  );  

        /**
         * If the actual user can not update the post
         * GET OUT OF HERE
         */
        if( !current_user_can('publish_posts') )
            return wp_send_json_error( 'You are not allow to do this' );
        # ------------------------- SECURITY VALIDATION OFF ----------------------------- 


        # ------------------------ BUSINESS LOGIC ON ---------------------------------------
        #Create the request
        $day = $_POST['day'];

        if( $day == '4' )
            wp_send_json_success('Success');
        else
            wp_send_json_error('Only can publish on 4th, not on ' . $day);
        # ------------------------ BUSINESS LOGIC OFF --------------------------------------
    }
    
}# End class

$ajax_example = new ajax_example();
}