title: In ts I want a function's parameter to be of type string, but there can be several known strings as hints
body: <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-js lang-js prettyprint-override"><code>function fn(str: string | 'abc') {}
  
  fn('a'); // I want to get the prompt for abc after typing a</code></pre>
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  <p><a href="https://i.stack.imgur.com/SH7Nh.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/SH7Nh.png" alt="enter image description here" /></a></p>
  <p>I want to get the prompt for abc after typing a, what should I do.</p>