title: How to merge two subarrays in JavaScript without changing the order of the array
body: <p>I need to merge two subarrays inside an array without pushing them to the end of the array</p>
  <pre><code>let array = [[&quot;a&quot;], [&quot;b&quot;], [&quot;c&quot;], [&quot;d&quot;]];
  array[1] = array[1].concat[2];
  </code></pre>
  <p>So I basically want <code>array</code> to be</p>
  <pre><code>array = [[&quot;a&quot;], [&quot;bc&quot;], [&quot;d&quot;]];
  </code></pre>
  <p>Thanks!</p>