title: What is the name of this special definition syntax in Javascript?
body: <p>I was reading the ReactJS source code in Github and I noticed that the React team use an special syntax when they define a type.</p>
  <p>The special syntax looks like this:</p>
  <pre><code>type Example = {|
    id: string
  |};
  </code></pre>
  <p>Is the <code>{| |}</code> part of the type definition a Javascript named feature? Or Is it something related to the use of a typing extension (Flow/Typescript) in the React codebase?</p>
  <p>In any case I really want to know the name of this feature whether if it's directly related to Javascript or not because after an extensive research in Google I couldn't find anything.</p>