How to re-render the view when the browser is resized?

You can use the useState hook to manage the width and height state variables, and the useEffect hook to add and remove the resize event listener. The [] dependency array passed to useEffect ensures that the effect only runs once (on mount) and not on every re-render.

    import React, { useState, useEffect } from "react";
    function WindowDimensions() {
      const [dimensions, setDimensions] = useState({
        width: window.innerWidth,
        height: window.innerHeight,
      });

      useEffect(() => {
        function handleResize() {
          setDimensions({
            width: window.innerWidth,
            height: window.innerHeight,
          });
        }
        window.addEventListener("resize", handleResize);
        return () => window.removeEventListener("resize", handleResize);
      }, []);

      return (
        <span>
          {dimensions.width} x {dimensions.height}
        </span>
      );
    }
    

<details>
<summary><h4>Using Class Component</h4></summary>

You can listen to the resize event in componentDidMount() and then update the dimensions (width and height). You should remove the listener in componentWillUnmount() method.

    class WindowDimensions extends React.Component {
      constructor(props) {
        super(props);
        this.updateDimensions = this.updateDimensions.bind(this);
      }

      componentWillMount() {
        this.updateDimensions();
      }

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

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

      updateDimensions() {
        this.setState({
          width: window.innerWidth,
          height: window.innerHeight,
        });
      }

      render() {
        return (
          <span>
            {this.state.width} x {this.state.height}
          </span>
        );
      }
    }
    

</details>

> Modern React Note: componentWillMount, componentWillReceiveProps, and componentWillUpdate are legacy lifecycles deprecated since React 16.3 and removed in modern React. In modern functional React, use the useEffect Hook or derive state values directly during render.