title: what is const/type pattern in Typescript
body: <pre><code>export const INCREMENT_ENTHUSIASM = 'INCREMENT_ENTHUSIASM';
  export type INCREMENT_ENTHUSIASM = typeof INCREMENT_ENTHUSIASM;
  
  
  export const DECREMENT_ENTHUSIASM = 'DECREMENT_ENTHUSIASM';
  export type DECREMENT_ENTHUSIASM = typeof DECREMENT_ENTHUSIASM;
  </code></pre>
  
  <p>what is happening here? I am not able to understand this.It is very confusing
  This is from here  <a href="https://github.com/Microsoft/TypeScript-React-Starter" rel="noreferrer">https://github.com/Microsoft/TypeScript-React-Starter</a> under <strong>Adding actions</strong> section.</p>
  
  <p>I know what <strong>type</strong> keyword do but it seems very confusing here.</p>
  
  <p><a href="https://i.stack.imgur.com/fiuhY.png" rel="noreferrer"><img src="https://i.stack.imgur.com/fiuhY.png" alt="enter image description here"></a></p>