useEffect3.js

import React, { Component } from "react";

class MyComponent extends UseEffectExample {
  constructor(props) {
    super(props);
    this.state = {
     width: window.innerWidth;
    };
  }

  componentDidMount() {
    window.addEventListener("resize", this.handleResize);
  }

  componentWillUnmount() {
    window.removeEventListener("resize", this.handleResize);
  }

  handleResize = () =>{
    this.setState({ width: window.innerWidth });
  }

  render() {
    return (
      <h1>{this.state.width}</h1>
    );
  }
}