Good question...!

So you need to do something like this:

constructor(props){
    super(props);
    this.state = {
      data: [],
      total:null,
      currentCount:3,
      offset:3,
    };
this.loadOnScroll = this.loadOnScroll.bind(this);
this.loadInitialContent = this.loadInitialContent.bind(this);
}

componentDidMount () {
    window.addEventListener('scroll', this.loadOnScroll);
  }

  componentWillMount(){
    this.loadInitialContent();
  }

  loadInitialContent(){
    fetch(  APIurl  , {
      method: "GET",
      headers: {
        "Content-Type": "application/json"
      },
      credentials: "same-origin" })
      .then(
      response => response.json()
    ).then(
      myData => {
        let ary =  myData.slice(0,this.state.offset)
        this.setState({ data: ary, list: myData, total: myData.length });

      }
    )
  }

  componentWillUnmount(){
    window.removeEventListener('scroll', this.loadOnScroll);
  }

  loadOnScroll = (e) =>{
    //If all the content loaded
    if(this.state.currentCount >= this.state.total) return;

    //Get div at the bottom of the content
    var el = document.getElementById('content-end');

    if(el) {
      var rect = el.getBoundingClientRect();
      var isAtEnd = (
          rect.bottom <= (window.innerHeight || document.documentElement.clientHeight) && /*or $(window).height() */
          rect.right <= (window.innerWidth || document.documentElement.clientWidth) /*or $(window).width() */
      );

      //User at the end of content. load more content
      if(isAtEnd){
        //If content list is still loading do not request for another content list.
        if(this.state.isFetching) return
        this.setState({isFetching:true});
          var count = this.state.currentCount + this.state.offset
          if(this.state.currentCount <= this.state.total){
            this.setState({
              isFetching:false,
              currentCount:count,
              data: this.state.list.slice(0, count)
            })
          }
      }
  }

render() {
    return (
<section>
      <div className="content">
      your contents here ....
     </div>
     <div id="content-end" >
            { /* Start load more content when this div is visible*/
              (this.state.currentCount <= this.state.total && this.state.isFetching)? <span>Loading Content...!!</span>
              : null
            }
    </div>
  </section>