WordPress ajax plugin example

wp-ajax-plugin-example.php

Replace name_of_action with the name of the ajax action;
Replace name-of-plugin and name_of_plugin with the name of the plugin

File: name-of-plugin.php
<?php

class name_of_plugin {
  /**
   * Setup
   */
  static function setup {
    self::_include( 'name-of-plugin-ajax' );
    name_of_plugin_ajax::setup();
  }

  /**
   * Include
   * Helper method to load class files
   * @param  string $class
   */
  static function _include( $class ) {
    require_once __DIR__ ."/includes/class-{$class}.php";
  }

  /**
   * Get plugin URL
   * @param  string $path
   * @return string
   */
  static function get_plugin_url( $path = '' ) {
    return plugin_dir_url( __FILE__ ) . $path;
  }
}
name_of_plugin::setup();

?>

File: includes/class-name-of-plugin-ajax.php
<?php

class name_of_plugin_ajax {

  /**
   * Setup
   */
  static function setup() {
    $action = 'name_of_action';
    add_action( 'wp_enqueue_scripts', __CLASS__ .'::enqueue_scripts' );
    add_action( 'wp_ajax_name_of_action', __CLASS__ .'::name_of_action' );
    add_action( 'wp_ajax_nopriv_name_of_action', __CLASS__ .'::name_of_action' );
  }

  /**
   * Enqueue scripts
   */
  static function enqueue_scripts() {
    // Register the script
    wp_register_script( 'name_of_plugin', name_of_plugin::get_plugin_url() .'assets/name-of-plugin.js' );

    // Localize the script with new data
    wp_localize_script( 'name_of_plugin', 'name_of_plugin', [
      'ajax_url' => admin_url( 'admin-ajax.php' ),
    ] );

    // Enqueued script with localized data.
    wp_enqueue_script( 'name_of_plugin' );
  }

  static function name_of_action() {
    // Use $_POST data to get data from the ajax call
    $json = json_encode( /* Code here */ );
    header('Content-Type: application/json');
    die( $json );
  }
}

?>

File: assets/name-of-plugin.js
jQuery( function() {
  
  $.post( name_of_plugin.ajax_url, {
    action: name_of_action,
    // .. other post data here
  }, function( data ) {
    // .. do stuff with data here
  } );
} );