title: "have no overlap" error while comparing enum values in TypeScript
body: <p>I'm trying to learn TypeScript and had been following online tutorial examples for enum support in TypeScript. For this below snippet:</p>
  
  <pre><code>enum daysoftheweek{
      SUN, MON, TUE, WED, THU, FRI, SAT
  }
  
  let day:daysoftheweek ;
  
  day = daysoftheweek.FRI; //line 7
  
  if (day === daysoftheweek.MON){
      console.log("got to go to work early");
  }else{
      console.log("I may go late");
  }
  </code></pre>
  
  <p>...I'm getting this error at compile time and I don't understand why:</p>
  
  <blockquote>
    <p><strong>TS2367:</strong> This condition will always return 'false' 
    since the types 'daysoftheweek.FRI' and 'daysoftheweek.MON' have no overlap.</p>
  </blockquote>
  
  <p>If I modify line 7 to this, the error goes off:
  <code>day = daysoftheweek.MON;</code></p>
  
  <p>Can somebody please explain why compilation is throwing that error?<br>
  (I followed other threads on this "have no overlap" error , but couldn't understand the reason for this particular snippet's problem)</p>