Fuse has built-in support for launching the importer within a modal. Simply pass the modal: true option when you instantiate your importer.

const importerOptions = {
  modal: true 
};

const importer = new FuseImporter({ options: importerOptions });

importer.getSessionToken = ... // see https://fuse-docs.flatirons.com/getting-started/sessions

importer.show();