What is the meaning of !! in ReactJS / JSX

Question

I'm new to react and I was reading about using transition and I stumbled on this article, which has few demo and saw this part of the code:

render() {
    const { show } = this.state
    return (
      <div>
        <button onClick={() => this.handleToggle()}>
          Click to toggle
        </button>
        <div>
          <Fade in={!!show} />
        </div>
      </div>
    )
}

What does it mean by two !!? It seems I can't find any docs about this symbol. I'm thinking this is a JSX syntax.

<Fade in={!!show} />