title: Push a dimensional array
body: <p>Why the answer is undefined in the Second example?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>// First
  var arr = [
    [1, 4, 6],
    ['alex']
  ];
  var newArr = arr[1];
  newArr.push('Peter');
  console.log(arr);
  
  // Second
  var arr = [
    [1, 4, 6],
    ['alex']
  ];
  arr.push([1]['Peter']);
  console.log(arr);</code></pre>
  </div>
  </div>
  </p>