onclick react

import React, { Component } from 'react';

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

  sayHello() {
    alert('Hello!');
  }
  
  return (
    <button onClick={this.sayHello}>
      Click me!
    </button>
  );
}

export default App;

change:
  <button type="button" onClick={this.myFunction(argument)}> myButton </button>
  
to this: 
  <button type="button" onClick={this.myFunction.bind(this, argument)}> myButton </button>

import React from 'react';

const App = () => {
  
const message = () => {
 console.log("Hello World!") 
}

return (
<button onClick={message}> Press me to print a message! </button>
  );
}

import React from 'react';

function App() {

  function sayHello() {
    alert('Hello!');
  }
  
  return (
    <button onClick={sayHello}>
      Click me!
    </button>
  );
}

export default App;

function ActionLink() {
  function handleClick(e) {    e.preventDefault();    console.log('The link was clicked.');  }
  return (
    <a href="#" onClick={handleClick}>      Click me
    </a>
  );
}

//Event hadling in react
function ActionLink() {
  function handleClick(e) {
    e.preventDefault();
    console.log('The link was clicked.');
  }

  return (
    <a href="#" onClick={handleClick}>
      Click me
    </a>
  );
}

<button onClick={sayHello}>Click</button>

var Box = React.createClass({
  getInitialState: function() {
    return {windowWidth: window.innerWidth};
  },

  handleResize: function(e) {
    this.setState({windowWidth: window.innerWidth});
  },

  componentDidMount: function() {
    window.addEventListener('resize', this.handleResize);
  },

  componentWillUnmount: function() {
    window.removeEventListener('resize', this.handleResize);
  },

  render: function() {
    return <div>Current window width: {this.state.windowWidth}</div>;
  }
});

ReactDOM.render(<Box />, mountNode);