title: What do {curly braces} around javascript variable name mean
body: <p><strong>EDIT</strong>
  After looking at JSHint I found this '<strong>destructuring expression' is available in ES6 (use esnext option) or Mozilla JS extensions (use moz)</strong> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/New_in_JavaScript/1.7" rel="noreferrer">this</a>  however after reading it I still don't understand why it is used </p>
  
  <p>I have come across the following code on <a href="https://developer.mozilla.org/en-US/Add-ons/SDK/High-Level_APIs/ui" rel="noreferrer" title="MDN">MDN</a></p>
  
  <pre><code>var ui = require("sdk/ui");
  var { ActionButton } = require("sdk/ui/button/action");
  </code></pre>
  
  <p>What do the braces on the second line do and why are they used? Why are there no braces on the first line?</p>