Question: I am trying to call a function inside an arrow function but somehow it doesn't work. What am I doing wrong?

This doesn't work:

```
restartVideo(ref){
 ref.player.seek(0)
}

onProgress={() => {this.state.restart ? this.restartVideo : null}}

```

This does:

```
onProgress={() => {this.state.restart ? ref.player.seek(0) : null}}

```

Whole component:

```
<Video source={video}   // Can be a URL or a local file.
       ref={ref => this.player = ref} // Store reference
       rate={1.0}                     // 0 is paused, 1 is normal.
       paused={this.state.paused}                 // Pauses playback entirely.
       onLoadStart={this.loadStart}   // Callback when video starts to load
       onProgress={() => {this.state.restart ? this.restartVideo : null}}      // Callback every ~250ms with currentTime
       onEnd={this.backToQuestion}             // Callback when playback finishes
       onError={this.videoError}      // Callback when video cannot be loaded
       style={styles.video} />

```

Event a `console.log()` is not fired inside `restartVideo()`

Answer: 
Change

```
onProgress={() => {this.state.restart ? this.restartVideo : null}}

```

to

```
onProgress={() => {this.state.restart ? this.restartVideo() : null}}

```

i.e. assign a function that *calls* `this.restartVideo`, rather than one that returns it.

By the way, it looks as though you should also be passing `ref` (or accessing it via `this` in the function).
if you put parenthesis in this line:

> 
> onProgress={() => {this.state.restart ? this.restartVideo() : null}}
> 
> 
> 

you can see this jsfiddle, I try to make something similar based on you code:
<https://jsfiddle.net/69z2wepo/63824/> 

```
class VideoContainer extends React.Component {
  constructor(props) {
    super(props);

    this.state = {
      restart: false
    }
  }

  componentDidMount(){
   setTimeout(function() { this.setState({restart: true}); }.bind(this), 3000);
  }

  restartVideo() {
    console.log('Video restarting...')
  }

  render() {
    return (
      <video
      width="400" controls
      src="http://www.quirksmode.org/html5/videos/big_buck_bunny.webm"
       onProgress={() => {this.state.restart ? this.restartVideo() : null}}      
      />
    )
  }
}

ReactDOM.render(
  <VideoContainer  />,
  document.getElementById('container')
);

```

I hope you that helps you