add a function call to a react component handler code example

Example 1: react button onclick

import React, { Component } from 'react';

class App extends Component {
  
  constructor(props) {
    super(props);
    this.sayHello = this.sayHello.bind(this);
  }

  sayHello() {
    alert('Hello!');
  }
  
  return (
    
      Click me!
    
  );
}

export default App;

Example 2: react native function

class Foo extends Component {
  handleClick() {
    console.log('Click happened');
  }
  render() {
    return Click Me;
  }
}