title: What is "export default" in JavaScript?
body: <p>File: <a href="https://github.com/wycats/handlebars.js/blob/583141de7cb61eb70eaa6b33c25f475f3048071b/lib/handlebars/safe-string.js" rel="noreferrer">SafeString.js</a></p>
  <pre><code>// Build out our basic SafeString type
  function SafeString(string) {
    this.string = string;
  }
  
  SafeString.prototype.toString = function() {
    return &quot;&quot; + this.string;
  };
  
  export default SafeString;
  </code></pre>
  <p>I have never seen <code>export default</code> before. Are there any equivalent stuff for <code>export default</code> that can be easier to understand?</p>