IE11 add/remove/contains class for SVG

ie11svg.js

if (!("classList" in SVGElement.prototype)) {
  Object.defineProperty(SVGElement.prototype, "classList", {
    get() {
      return {
        contains: className => {
          return this.className.baseVal.split(" ").indexOf(className) !== -1;
        },
        add: className => {
          return this.setAttribute('class', this.getAttribute('class') + ' ' + className);
        },
        remove: className => {
          var removedClass = this.getAttribute('class').replace(new RegExp('(\\s|^)' + className + '(\\s|$)', 'g'), '$2');
          if (this.classList.contains(className)) {
            this.setAttribute('class', removedClass);
          }
        }
      };
    }
  });
}

I saw that but don't get how to implement in the original gist