Why is the scroll event not firing?

Question

JavaScript

There is this component:

class App extends React.Component {

  constructor() {
    super();

    window.onscroll = function() {
      console.log(1);
    }

  }

  componentDidMount() {
    window.onscroll = function() {
      console.log(1);
    }
  }



  render() {
    window.onscroll = function() {
      console.log(1);
    }
  }
}

Why isn't the scroll event fired anywhere?

Answer 1

Apparently, because the page does not have the ability to scroll. All content is placed in the height of the window.
If so, then for such cases use the mousewheel event. For cross-browser handling of this event, if the same scroll speed in different browsers is important, you need to use an adapter, like normalize-wheel

Answer 2

try like this

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

  componentWillUnmount() {
    window.removeEventListener('scroll', this.handleScroll);
  }
   
  
  handleScroll = () => {
    alert("scroll");
  };