Ajax before send question

Hello,

Is it safe or ok to alter the, I mean I going copy this code in my custom module (.js file) and add some conditions. Is this ok?

/**
 * Prepare the Ajax request before it is sent.
 */
Drupal.ajax.prototype.beforeSend = function (xmlhttprequest, options) {
  // For forms without file inputs, the jQuery Form plugin serializes the form
  // values, and then calls jQuery's $.ajax() function, which invokes this
  // handler. In this circumstance, options.extraData is never used. For forms
  // with file inputs, the jQuery Form plugin uses the browser's normal form
  // submission mechanism, but captures the response in a hidden IFRAME. In this
  // circumstance, it calls this handler first, and then appends hidden fields
  // to the form to submit the values in options.extraData. There is no simple
  // way to know which submission mechanism will be used, so we add to extraData
  // regardless, and allow it to be ignored in the former case.
  if (this.form) {
    options.extraData = options.extraData || {};

    // Let the server know when the IFRAME submission mechanism is used. The
    // server can use this information to wrap the JSON response in a TEXTAREA,
    // as per http://jquery.malsup.com/form/#file-upload.
    options.extraData.ajax_iframe_upload = '1';

    // The triggering element is about to be disabled (see below), but if it
    // contains a value (e.g., a checkbox, textfield, select, etc.), ensure that
    // value is included in the submission. As per above, submissions that use
    // $.ajax() are already serialized prior to the element being disabled, so
    // this is only needed for IFRAME submissions.
    var v = $.fieldValue(this.element);
    if (v !== null) {
      options.extraData[this.element.name] = v;
    }
  }

  // Disable the element that received the change to prevent user interface
  // interaction while the Ajax request is in progress. ajax.ajaxing prevents
  // the element from triggering a new request, but does not prevent the user
  // from changing its value.
  $(this.element).addClass('progress-disabled').attr('disabled', true);

  // Insert progressbar or throbber.
  if (this.progress.type == 'bar') {
    var progressBar = new Drupal.progressBar('ajax-progress-' + this.element.id, eval(this.progress.update_callback), this.progress.method, eval(this.progress.error_callback));
    if (this.progress.message) {
      progressBar.setProgress(-1, this.progress.message);
    }
    if (this.progress.url) {
      progressBar.startMonitoring(this.progress.url, this.progress.interval || 1500);
    }
    this.progress.element = $(progressBar.element).addClass('ajax-progress ajax-progress-bar');
    this.progress.object = progressBar;
    $(this.element).after(this.progress.element);
  }
  else if (this.progress.type == 'throbber') {
    this.progress.element = $('<div class="ajax-progress ajax-progress-throbber"><div class="throbber">&nbsp;</div></div>');
    if (this.progress.message) {
      $('.throbber', this.progress.element).after('<div class="message">' + this.progress.message + '</div>');
    }
    $(this.element).after(this.progress.element);
  }
};

I tried it and it's working and I don't have problem so far. I just want to make sure I'm not doing it badly.

Any suggestions or advices will be appreciated.

Thanks,
Darryl