Why does this return a number?
<p>Why does this code print out <code>4</code> rather than <code>['B', 'e', 'e', 'a']</code>?</p>

<pre><code>var word = 'Bee';
var letters = word.split('').push('a');

console.log(letters);
// -&gt; 4
</code></pre>