如何修复滚动显示div（反应）

Question

After i set some div to show after scroll, the result is the div is not hidden when the page is open(or reload)

I have tried to have the - componentWillMount, and - componentDidMount for the lifecycle, but i got the same result

This is the code

1. Initiate the state

constructor(props){
    super(props);
    this.state={
      isHide:false,
    };
    this.hideBar = this.hideBar.bind(this)
  }

2. Make the function

 hideBar(){
    let {isHide} = this.state;
    window.scrollY < 300 && this.prev ?
    !isHide && this.setState({isHide:true})
    :
    isHide && this.setState({isHide:false})
    this.prev = window.scrollY;
  }

  componentWillMount(){
      window.addEventListener('scroll',this.hideBar);
  }
  componentWillUnmount(){
       window.removeEventListener('scroll',this.hideBar);
  }

3. Calling the function

render() {
    let classHide=this.state.isHide?"newsletterhide":""
      return (
        <div className={classHide+"newsletter-container"}>
          <div className="newsletter-details">
            <h3 style={{margin:0, fontSize:"0.9em"}}>
              Get latest updates in web technologies
            </h3>
            <p className="p-newsletter">
              I write articles related to web technologies, such as design trends, development tools, UI/UX case studies and reviews, and more. Sign up to my newsletter to get them all.
            </p>
          </div>
          <div className="newsletter-form">
            <input 
              name="email" 
              type="email" 
              placeholder="Email address" 
              className="newsletter-input"
            />
            <button className="newsletter-button">
              Count me in!
            </button>
          </div>
        </div>
    );
  }

Thanks for your help!, hope the other who need it find it useful.

Answer 1

As I understood, you want to show subscribe to newsletter box when user scrolls down in the page. Why don't you just write:

hideBar() {
  this.setState({
    isHidden: window.scrollY < 300
  });
}

And setting isHidden to true at the beginning should solve your problem. If not, then call hideBar method at componentDidMount .

And also, I recommend that you show the newsletter box after user spend some time looking at the website; eg show it 15 seconds after he/she reads the article.

Answer 2

Assuming the problem is during reloads there being a page offset and your intension is to show the div then,

componentDidMount() {
  if(window.pageYOffset) this.setState({ isHide: false, });
}