title: Typescript change object value type to string literal
body: <p>Is it possible to change object value type to string literal without type assertion?</p>
  
  <p>e.g.:</p>
  
  <pre><code>const foo = {
      bar: 'foobar',
  }; // =&gt; typeof foo is { bar: string }
  </code></pre>
  
  <p>is it possible to change this to <code>{ bar: 'foobar' }</code> type without type assertion?</p>