Event timeline with animation

I’ve modified your sandbox to make it work:
https://codesandbox.io/s/animable-timeline-reactjs-tiofz

1. For animation I used following CSS:

   div {
     height: 200px;
     width: 10px;
   }
   
   .green-progress {
     background: linear-gradient(0, #00a36c, #00a36c) no-repeat, #ccc;
     background-size: 100% 0;
     animation: progressAnim 3s linear infinite forwards;
   }
   
   @keyframes progressAnim {
     0% {
       background-size: 100% 0;
     }
     100% {
       background-size: 100% 100%;
     }
   }

   <div class="green-progress"></div>

   To animate actual time line we’ll remove vertical bar from first entry and there will be only checked circle. From second entry onwards we’ll have a vertical bar and checked circle. To make them consistent they’ve been shifted upwards. To show progress, the bar will fill and then circle will be checked.

2. Converted App to stateful component so that we can maintain animation states.
   In constructor, for each entry added id, startAnim, and checked state. Here, we’ll set startAnim flag to start animation on corresponding TimelineConnector. and checked is used to control checkmarking the circle.

3. In TimelineConnector set class to green-progress if this.props.startAnim is true. Also added onAnimationEnd handler as {() => this.props.onAnimDone(this.props.id)}. This tells App component that animation is done on this component with id.

4. In TimelineDot used props.event.checked to set the checked status.

5. In App added a lifecycle hook componentDidMount which will get called when all components gets added to actual DOM. In the hook you checkmark the first circle and start animation on first TimelineConnector.

6. When TimelineConnector is done with the animation, it calls startNextAnim in the App. In the method you first complete the checkmark on last entry. And start next animation if the entry has status:true.

We could’ve added delays to each animation and ran them at once. But parent controlling each component and each component notifying when animation is done makes it more flexible to update the code. You can have different animations for each entry, based on their state.

We can use react-spring animation library but things will get complicated. CSS animation is the simplest solution.