bind argument without effecting this

bind.tsx

class PoseSwiper extends Component<Props> {
  state = {
    activeIndex: 0
  };
  config = {
    slidesPerView: 1,
    observer: true,
    on: {
      slideChange: function(applyNewIndex: (index: number) => void) {
        applyNewIndex(this.activeIndex);
      }
    }
  };
  
  constructor(props) {
    super(props);
    const method = this.config.on.slideChange;
    const onIndexChange = this.setIndex;
    this.config.on.slideChange = function() {
      method.bind(this, onIndexChange)();
    };
  }
  
  setIndex = (index: number) => {
    this.setState((prev) => ({ ...prev, activeIndex: index }));
  };
}