CODEWITHSUNDEEP
javascriptreactjs
user12855683
user12855683

Reputation:

React Infinity scrool : TypeError: Cannot read property 'offsetTop' of null

I am trying to implement an infinity scroll but facing the "TypeError: Cannot read property 'offsetTop' of null". I have attached my implementation below. I am new to react and I would love to get your suggestion for better implementation.

     loadMore = () => {

       this.setState({page: this.state.page + 1})
       this.loadUser();
      };

      handleScroll = () => { 
        var lastLi = document.querySelector("div.container-fluid > div:last-child");
        var lastLiOffset = lastLi.offsetTop + lastLi.clientHeight;
        var pageOffset = window.pageYOffset + window.innerHeight;
      if (pageOffset > lastLiOffset) {
             this.loadMore();
        }
      };

    componentWillMount() {
        this.loadUser();
        this.scrollListener = window.addEventListener("scroll", e => {
            this.handleScroll(e);
          });
     }

    render() {

        if(this.state.dataStatus == false) {
            return (
                <div>
             <Header />   
                <h4>Loading</h4>

            </div>
            );
        } else {
        return(
            <div>
        <Header />   
            <PostContainer posts={this.state.data}/> 

        </div>
        );
        }
    }
}

PostContainer Code -> it traverses through the array and calls Renderpost

class PostContainer extends Component {

constructor(props) {
    super(props);
}

      render() {

           const menu = this.props.posts.map(post => {
            return (

                <RenderPost post={post}/>
            )
            });

          return (
            <div className="container-fluid">
            <div className="row justify-content-center">
               {menu}
            </div>
        </div>
          );
      }

}

RenderPost code

 return(

                <div className="post-holder shadow-sm p-3 mb-4 bg-white rounded" key={this.props.post.id}>

            </div>
           );

Upvotes: 0

Views: 96

Answers (2)

Drew Reese
Drew Reese

Reputation: 203323

document.querySelector can return null if there are no matches. You should definitely check if a valid HTMLElement was returned before accessing attributes on it.

Also, I think the selector "div.container-fluid > div:last-child" will more likely match the <div className="row justify-content-center"> div as it is the direct child of "div.container-fluid".

Instead, it looks like you want to target the last post that is rendered by this inner div. Using an id may make this easier

<div className="row justify-content-center" id="post-container">
  {menu}
</div>

Then update the handler

var lastLi = document.querySelector("div#post-container > div:last-child");

Upvotes: 1

shai_sharakanski
shai_sharakanski

Reputation: 417

try to learn about ref, in React.js we don't use querySelector

Upvotes: 0

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