title: Array.prototype.find() is undefined
body: <p>In <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/find" rel="nofollow">here</a></p>
  
  <p>it says that this should work:</p>
  
  <pre><code>function isPrime(element, index, array) {
      var start = 2;
      while (start &lt;= Math.sqrt(element)) {
          if (element % start++ &lt; 1) return false;
      }
      return (element &gt; 1);
  }
  
  console.log( [4, 5, 8, 12].find(isPrime) ); // 5
  </code></pre>
  
  <p>But I end up having an error:</p>
  
  <pre><code>TypeError: undefined is not a function
  </code></pre>
  
  <p>Why is that?</p>
  
  <p>P.S.     </p>
  
  <p><em>I'm trying not to use <a href="http://underscorejs.org/" rel="nofollow">underscorejs</a> library since the browsers are supposed to support functions like <code>find()</code> already.</em></p>