silverstripe-webpack/site/src/js/_components/_spinner.js

/**
 * Just an example component
 */
import $ from 'jquery';

const SpinnerUI = (($) => {
    class SpinnerUI {
        static show(callback) {
            $('#PageLoading').show(0, callback);
        }

        static hide(callback) {
            $('#PageLoading').hide('slow', callback);
        }
    }
    return SpinnerUI;
})($);

export default SpinnerUI;