title: Restrict array's value in TypeScript
body: <p>I want my placement prop can have any string inside array but I want to restrict it to have only four values. I have created an enum though it would work it seems a wrong way. How can we achieve this in typescript?</p>
  
  <pre><code>export enum Placement {
    RIGHT = 'right',
    LEFT = 'left',
    TOP = 'top',
    bottom = 'bottom'
  }
  
  interface IProps {
    className?: string;
    placement: string[]; // Placement []
  }
  </code></pre>