How to use the @uirouter/core.isFunction function in @uirouter/core

handleClick = e => {
    const childOnClick = this.props.children.props.onClick;
    if (isFunction(childOnClick)) {
      childOnClick(e);
    }

    if (!e.defaultPrevented && !(e.button == 1 || e.metaKey || e.ctrlKey)) {
      e.preventDefault();
      let params = this.props.params || {};
      let to = this.props.to;
      let options = this.getOptions();
      this.props.router.stateService.go(to, params, options);
    }
  };

return () => {
      if (isFunction(cleanup.current)) cleanup.current();
    };
  }, []);