Create modal window in drupal 8 using Drupal.dialog function

drupal.dialog.js

/** EXAMPLE 1 ***/
var $myDialog = $('<div>My dialog text</div>').appendTo('body');
Drupal.dialog($myDialog, {
  title: 'A title',
  buttons: [{
    text: 'Close',
    click: function() {
      $(this).dialog('close');
    }
  }]
}).showModal();

/** EXAMPLE WITH AJAX **/
Drupal.ajax({
  url: 'some/path',
  success: function(response) {
    var $myDialog = $('<div>' + response.data + '</div>').appendTo('body');
    Drupal.dialog($myDialog, {title: 'Some title'}).showModal();
  }
}).execute();

Nice, but one can't possibly reproduce the contents of a whole form inside the $myDialog variable. Isn't there a way of pointing this dialog to a route or url instead?

Secondly, I am trying to open an off-canvas dialog and this doesn't work for that. Pls how do I do that? My requirements need me to open that off-canvas when a checkbox is enabled...

@ilechcod Yes. This is just how to work with simple HTML snippets.

If you want to do AJAX, you probably want:
https://www.drupal.org/docs/drupal-apis/ajax-api/ajax-dialog-boxes