title: Typescript initialise a type with initial/ default value
body: <p>Is it possible to create a <code>Type</code> with value in it.</p>
  
  <p>eg: </p>
  
  <pre><code>type Animal = {
      kind : "animal"
      Legs : number,
      CanFly: boolean
  }
  
  const monkey: Animal = { Legs: 4, CanFly: false};  //In this line, clients has to initialize the same value `kind : "animal"`
  </code></pre>
  
  <p>I would to create an attribute called kind and use that to infer the object and make decisions.
  However, in the next line, i would expect the clients to pass the same value back in all the initializations. Otherwisem TS compiler would complain `Property 'kind' is missing in type'.</p>
  
  <p>Is there a way to default it without the clients have to pass it back?</p>