old_contents: import React from "react";
  import ReactDOM from "react-dom";
  import Clipboard from "react-clipboard";
  
  class Mouse extends React.Component {
    handleMove = ({ clientX, clientY }) => {
      this.props.onMove({ x: clientX, y: clientY });
    };
  
    componentDidMount() {
      document.addEventListener("mousemove", this.handleMove);
    }
  
    componentWillUnmount() {
      document.removeEventListener("mousemove", this.handleMove);
    }
  
    render() {
      return nutll;
    }
  }
  
  class App extends React.Component {
    state = {
      pos: {
        x: 0,
        y: 0
      },
      copied: false
    };
  
    handleCopy = () => {
      clearTimeout(this.timer);
      this.setState({ copied: true });
      this.timer = setTimeout(() => this.setState({ copied: false }), 1000);
    };
  
    handleMove = pos => {
      this.setState({ pos });
    };
  
    render() {
      const { pos, copied } = this.state;
      const value = JSON.stringify(pos, null, "  ");
  
      return (
        <div>
          <Mouse onMove={this.handleMove} />
          <p>Press Cmd + C to copy mouse position</p>
          <pre>
            ({pos.x},{pos.y})
          </pre>
          <Clipboard value={value} onCopy={this.handleCopy} />
          {copied && <p>copied</p>}
        </div>
      );
    }
  }
  
  ReactDOM.render(<App />, document.querySelector("#app"));
  
new_contents: import React from "react";
  import ReactDOM from "react-dom";
  import Clipboard from "react-clipboard";
  
  class Mouse extends React.Component {
    handleMove = ({ clientX, clientY }) => {
      this.props.onMove({ x: clientX, y: clientY });
    };
  
    componentDidMount() {
      document.addEventListener("mousemove", this.handleMove);
    }
  
    componentWillUnmount() {
      document.removeEventListener("mousemove", this.handleMove);
    }
  
    render() {
      return null;
    }
  }
  
  class App extends React.Component {
    state = {
      pos: {
        x: 0,
        y: 0
      },
      copied: false
    };
  
    handleCopy = () => {
      clearTimeout(this.timer);
      this.setState({ copied: true });
      this.timer = setTimeout(() => this.setState({ copied: false }), 1000);
    };
  
    handleMove = pos => {
      this.setState({ pos });
    };
  
    render() {
      const { pos, copied } = this.state;
      const value = JSON.stringify(pos, null, "  ");
  
      return (
        <div>
          <Mouse onMove={this.handleMove} />
          <p>Press Cmd + C to copy mouse position</p>
          <pre>
            ({pos.x},{pos.y})
          </pre>
          <Clipboard value={value} onCopy={this.handleCopy} />
          {copied && <p>copied</p>}
        </div>
      );
    }
  }
  
  ReactDOM.render(<App />, document.querySelector("#app"));
  
subject: fix typo in example app