Handling Event

• inline if with logical && operator

function Mailbox(props) {
  const unreadMessages = props.unreadMessages;

  return(
    <div>
      <h1>Hello!</h1>
      {
        unreadMessages.length > 0 &&
        <h2>
          You have {unreadMessages.length} unread messages.
        </h2>
      }
    </div>
  );
}

const messages = ["React", "Re: React", "Re: Re: React"];

ReactDOM.render(
  <Mailbox unreadMessages = { messages } />,
  document.getElementById("root")
)

• Returning null from a component's render method does not affact the firing of the component's lifecycle methods