onSubmitHandler(evt) {
      evt.preventDefault();
      if (this.submitButton.getAttribute('aria-disabled') === 'true') return;

      this.handleErrorMessage();

      this.submitButton.setAttribute('aria-disabled', true);
      this.submitButton.classList.add('loading');
      this.querySelector('.loading-overlay__spinner').classList.remove('hidden');

      const config = fetchConfig('javascript');
      config.headers['X-Requested-With'] = 'XMLHttpRequest';
      delete config.headers['Content-Type'];

      const formData = new FormData(this.form);
      if (this.cart) {
        formData.append('sections', this.cart.getSectionsToRender().map((section) => section.id));
        formData.append('sections_url', window.location.pathname);
        this.cart.setActiveElement(document.activeElement);
      }
      config.body = formData;
      console.log("Form data: " + formData);

      fetch(`${routes.cart_add_url}`, config)
        .then((response) => response.json())
        .then((response) => {
          if (response.status) {
            this.handleErrorMessage(response.description);

            const soldOutMessage = this.submitButton.querySelector('.sold-out-message');
            if (!soldOutMessage) return;
            this.submitButton.setAttribute('aria-disabled', true);
            this.submitButton.querySelector('span').classList.add('hidden');
            soldOutMessage.classList.remove('hidden');
            this.error = true;
            return;
          } else if (!this.cart) {
            window.location = window.routes.cart_url;
            return;
          }

          this.error = false;
          const quickAddModal = this.closest('quick-add-modal');
          if (quickAddModal) {
            document.body.addEventListener('modalClosed', () => {
              setTimeout(() => { this.cart.renderContents(response) });
            }, { once: true });
            quickAddModal.hide(true);
          } else {
            this.cart.renderContents(response);
          }
        })
        .catch((e) => {
          console.error(e);
        })
        .finally(() => {
          this.submitButton.classList.remove('loading');
          if (this.cart && this.cart.classList.contains('is-empty')) this.cart.classList.remove('is-empty');
          if (!this.error) this.submitButton.removeAttribute('aria-disabled');
          this.querySelector('.loading-overlay__spinner').classList.add('hidden');
        });
    }