onclick this react 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 (
    <button onClick={this.sayHello}>
      Click me!
    </button>
  );
}

export default App;

Example 2: react why onclick property function trigger without click

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