How to use the @material/textfield/foundation function in @material/textfield

mounted() {
    this.foundation = new MDCTextfieldFoundation(
      Object.assign(
        {
          addClass: className => {
            this.$set(this.rootClasses, className, true);
          },
          removeClass: className => {
            this.$delete(this.rootClasses, className);
          },
          hasClass: className => {
            this.$refs.root.classList.contains(className);
          },
          registerTextFieldInteractionHandler: (evtType, handler) => {
            this.$refs.root.addEventListener(evtType, handler);
          },
          deregisterTextFieldInteractionHandler: (evtType, handler) => {
            this.$refs.root.removeEventListener(evtType, handler);

mounted() {
    this.foundation = new MDCTextfieldFoundation(
      Object.assign(
        {
          addClass: className => {
            this.$set(this.rootClasses, className, true);
          },
          removeClass: className => {
            this.$delete(this.rootClasses, className);
          },
          hasClass: className => {
            this.$refs.root.classList.contains(className);
          },
          registerTextFieldInteractionHandler: (evtType, handler) => {
            this.$refs.root.addEventListener(evtType, handler);
          },
          deregisterTextFieldInteractionHandler: (evtType, handler) => {
            this.$refs.root.removeEventListener(evtType, handler);