title: What does `node --harmony` do?
body: <p>A node application has required me to run node with a harmony flag, like:</p>
  
  <pre><code>node --harmony app.js
  </code></pre>
  
  <p>What is this harmony flag? What does it do and why can't the app run without it?</p>
  
  <p>I've tried looking into node command-line options (<code>node --help</code>), but it doesn't provide any details either. Node docs weren't of any help either.</p>