export default class Child extends Component {
render(){
    return(
      <button
         onClick={this.props.onClick}
         className={this.props.fadeAway ? 'active' : ''}>
         {this.props.text}
      </button>
     )
   }
}

export default class Parent extends Component {
   constructor(props) {
   super(props);
   this.state = {
     selectedIndex: null,
   };
 }

  handleClick (selectedIndex) {
   this.setState({
    selectedIndex,
   });
  }

  render () {
    const array = ["Button 1","Button 2"];
    return (
     <div>
       {array.map((obj, index) => {
       const faded = this.state.selectedIndex === index;
       return <Child
       text={obj}
       fadeAway={faded}
       key={index}
       onClick={() => this.handleClick(index)} />
       })}
     </div>
     )
   }
 }