class ErrorModal {
  constructor() {
    this.modal = null;
    this.title = null;
    this.body = null;
  }

  init() {
    // Create the modal element and set its attributes
    this.modal = document.createElement("div");
    this.modal.classList.add("modal", "fade");
    this.modal.id = "errorModal";
    this.modal.tabIndex = "-1";
    this.modal.setAttribute("role", "dialog");
    this.modal.setAttribute("aria-labelledby", "errorModalLabel");
    this.modal.setAttribute("aria-hidden", "true");

    // Create the modal dialog element
    const modalDialog = document.createElement("div");
    modalDialog.classList.add("modal-dialog");
    modalDialog.setAttribute("role", "document");

    // Create the modal content element
    const modalContent = document.createElement("div");
    modalContent.classList.add("modal-content");

    // Create the modal header element
    const modalHeader = document.createElement("div");
    modalHeader.classList.add("modal-header");

    // Create the modal title element
    this.title = document.createElement("h5");
    this.title.classList.add("modal-title");
    this.title.id = "errorModalLabel";
    this.title.textContent = "Error";

    // Add the title element to the header
    modalHeader.appendChild(this.title);

    // Create the close button element
    const closeButton = document.createElement("button");
    closeButton.classList.add("btn-close");
    closeButton.setAttribute("type", "button");
    closeButton.setAttribute("data-bs-dismiss", "modal");
    closeButton.setAttribute("aria-label", "Close");

    // Add the close button to the header
    modalHeader.appendChild(closeButton);

    // Add the header to the content
    modalContent.appendChild(modalHeader);

    // Create the modal body element
    this.body = document.createElement("div");
    this.body.classList.add("modal-body");

    // Add the body to the content
    modalContent.appendChild(this.body);

    // Add the content to the dialog
    modalDialog.appendChild(modalContent);

    // Add the dialog to the modal
    this.modal.appendChild(modalDialog);

    // Add the modal to the document
    document.body.appendChild(this.modal);
  }

  show(code, message) {
    // Update the title and body of the modal
    this.title.textContent = `Error ${code}`;
    this.body.textContent = message;

    // Show the modal
    const modal = new bootstrap.Modal(document.getElementById("errorModal"));
    modal.show();
  }
}

(function() {
  // code to run automatically when script is loaded
  console.log("Hello, world!");

const errorModal = new ErrorModal();
errorModal.init();

    // Display the error in the modal
errorModal.show(1021, "Ciao, come va li?");

})();

//__________________________________________________________________________________

<div class="container shadow min-vh-100 py-2">
    <div class="row">
        <div class="col">
            <h2 class="font-weight-light">Hello Bootstrap 5 😊</h2>
            <p>
                This is a Bootstrap 5 starter example snippet!
            </p>
        </div>
    </div>
</div>