Drupal 7: How to execute custom javascript before submiting an #AJAX Form

I had a Drupal project where I need to submit a form without reloading the page so I used Form API #ajax parameter to execute my custom callback function and validate the form.

Sample FORM:

 
function MODULENAME_bid_form($form, &$form_state) {
  $prices = array(
    0 => t('Select a bid amount'),
    10000 => '+ P 10,000',
    20000 => '+ P 20,000',
    30000 => '+ P 30,000',
  );
  $form['wrapper'] = array(
   '#type' => 'container',
   '#prefix' => '<div id="bid-wrapper">',
   '#suffix' => '</div>',
  );
  $form['wrapper']['bid_price'] = array(
    '#type' => 'select',
    '#options' => $prices,
    '#required' => TRUE,
    '#default_value' => 0,
    '#disabled' => TRUE,
  );
  $form['wrapper']['submit'] = array(
    '#type' => 'submit',
    '#value' => t('Bid Now!'),
    '#disabled' => TRUE,
    '#ajax' => array(
      'callback' => 'MODULENAME_bid_form_callback',
      'wrapper' => 'box',
      'event' => 'click',
    ),
  );
  return $form;
}

The ajax callback:

function MODULENAME_bid_form_callback(&$form, &$form_state) {
  $commands = array();
  $commands[] = ajax_command_remove('#messages-wrap');
  $commands[] = ajax_command_before('#bid-wrapper', '<div id="messages-wrap">' . theme('status_messages') . '</div>');
  $commands[] = ajax_command_replace('.field-name-field-current-bid .field-item', '<div class="field-item">New item value</div>');
  return array('#type' => 'ajax', '#commands' => $commands); 
}

We also need to display an alert message before submitting the form asking if they want to continue or cancel.
Below is the code snippet that I used to prevent the execution of Drupal ajax when cancel is clicked.

 (function ($) {
  'use strict';
  Drupal.behaviors.ReplaceWithAnyTextYouWant = {
    attach: function (context, settings) {
        // 'edit-submit' is the element ID where you execute the #ajax.
        Drupal.ajax['edit-submit'].options.beforeSubmit = function(form_values, element_settings, options) {
          // If cancel is clicked, do not continue submitting.
          if (!confirm('Are you sure you want to continue?') {
            return false;
          }
        }
  };
})(jQuery); 

You can also use this method to run a client side validation before submitting the form.

There are parameters available on the beforeSubmit that we can use like the form_values.

form_values will return an object where it contains the submitted form name and values. We can extract the value by using the code below:

        Drupal.ajax['edit-submit'].options.beforeSubmit = function(form_values, element_settings, options) {
          var bid_price = 0;
          for (var key in form_values) {
            console.log(form_values[key]); // This will display the object values on the console log.
            if (form_values[key]['name'] == 'bid_price') {
              bid_price =  form_values[key]['value'];
            }
          }
        }