moretti

  const btn = document.createElement('button');
  btn.className = 'btn red';
  btn.onclick = function(event) {
   if (this.classList.contains('red')) {
     this.classList.remove('red');
     this.classList.add('blue');
   } else {
     this.classList.remove('blue');
     this.classList.add('red');
   }
  };

  class Button extends React.Component {
    state = { color: 'red' }
    handleChange = () => {
      const color = this.state.color === 'red' ? 'blue' : 'red';
      this.setState({ color });
    }
    render() {
      return (<div>
        <button 
           className=`btn ${this.state.color}`
          
        </button>
      </div>);
    }
  }

    const foo = ({ a = 2, b = 2, c = 3 } = {}) => a * b * c;
    const dict = {b: 4, c: 6};

    foo(); // 12
    foo(dict); // 48