How to use the @material/menu/foundation.MDCMenuFoundation.strings function in @material/menu

notifySelected: evtData => {
        const evt = {
          index: evtData.index,
          item: this.items[evtData.index],
        };
        this.$emit('change', false);
        this.$emit('select', evt);
        emitCustomEvent(
          this.$el,
          MDCMenuFoundation.strings.SELECTED_EVENT,
          evt,
        );
      },
      notifyCancel: () => {

notifySelected: evtData => {
        emitCustomEvent(this.$el, MDCMenuFoundation.strings.SELECTED_EVENT, {
          index: evtData.index,
          item: this.items[evtData.index],
        });

        this.$emit('select', {
          index: evtData.index,
          item: this.items[evtData.index],
        });
      },
    });

notifyCancel: () => {
        this.$emit('change', false);
        this.$emit('cancel');
        emitCustomEvent(this.$el, MDCMenuFoundation.strings.CANCEL_EVENT, {});
      },
      saveFocus: () => {