transition-snippet.js

renderOutputs() {
  return (
  <TransitionGroup>
    {this.state.shortenedUrls.map(UrlPair =>
      <CSSTransition
        key={UrlPair.id}
        timeout={300}
        classNames='latestOut'
      >
        <UrlOutput longUrl={UrlPair.longUrl}
                   shortUrl={UrlPair.shortUrl}
        />
      </CSSTransition>
    )}
  </TransitionGroup>
  );
}