CODE EXAMPLE FOR JAVASCRIPT

component will unmount

import React from 'react';
class ComponentOne extends React.Component {
 
  // Defining the componentWillUnmount method
  componentWillUnmount() {
    alert('The component is going to be unmounted');
  }
 
  render() {
    return <h1>Hello Geeks!</h1>;
  }
}
 
class App extends React.Component {
  state = { display: true };
  delete = () => {
    this.setState({ display: false });
  };
 
  render() {
    let comp;
    if (this.state.display) {
      comp = <ComponentOne />;
    }
    return (
      <div>
        {comp}
        <button onClick={this.delete}>
          Delete the component
        </button>
      </div>
    );
  }
}
 
export default App;