<TransitionGroup>
    items.map((item,index) => (
        <CSSTransition
            key={item.id}
            timeout={1000}
            classNames="fade"
                <ItemPreview item={item} />
         </CSSTransition>
    ))
</TransitionGroup>

.fade-enter{
    opacity: 0;
    visibility: hidden;
    transition: all ease 1s;
}

.fade-enter.fade-enter-active{
    opacity: 1;
    visibility: visible;
    transition: all ease 1s;
}

.fade-exit {
    visibility: visible;
    opacity: 0;
}

.fade-exit.fade-exit-active{
    opacity: 0;
    visibility: hidden;
    transition: all ease 1s;
}

render(){
    const { items } = this.props;
    let delay_index = -1;
    let delay_jump = 100;
    return (
        <TransitionGroup>
            items.map((item,index) => {
                delay_index += offer.isNew ? 1 : 0;
                const delay = Math.max(0, delay_index*100);

                return (
                    <CSSTransition
                        key={item.id}
                        timeout={1000 + delay}
                        classNames="fade">
                            <ItemPreview
                                item={item}
                                style={{transitionDelay: `${delay}ms`}} />
                    </CSSTransition>
                )
            })
        </TransitionGroup>
    )
}