title: Trying to title case all words in string
body: <p>I am trying to title case a string using the String.prototype function syntax. For some reason I am getting: TypeError: Cannot read property 'split' of undefined.</p>
  
  <p>Does anyone see what I'm doing wrong here?</p>
  
  <pre><code>    String.prototype.toJadenCase = function (str) {
      str.split(' ')
      .map(w =&gt; w[0].toUpperCase() + w.substr(1).toLowerCase())
      .join(' ')
      };
  
      var str = "How can mirrors be real if our eyes aren't real";
  
      console.log(str.toJadenCase())
  </code></pre>