Method class

src/dom/p5.Element.js:471–478

* @return {String} element's classes, if any.

(c)

   * @return {String} element's classes, if any.
   */
  class(c) {
    if (typeof c === 'undefined') {
      return this.elt.className;
    }

    this.elt.className = c;
    return this;
  }

  /**
   *