title: Cannot redeclare block scoped variable
body: <p>I'm building a node app, and inside each file in .js used to doing this to require in various packages.</p>
  
  <pre><code>let co = require("co");
  </code></pre>
  
  <p>But getting </p>
  
  <p><a href="https://i.stack.imgur.com/Dgrz2.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Dgrz2.png" alt="enter image description here"></a></p>
  
  <p>etc. So using typescript it seems there can only be one such declaration/require across the whole project? 
  I'm confused about this as I thought <code>let</code> was scoped to the current file.</p>
  
  <p>I just had a project that was working but after a refactor am now getting these errors all over the place.</p>
  
  <p>Can someone explain?</p>