title: How to add an new array to an existing array and return a new array in JavaScript?
body: <p>I'm trying to add an new array to an existing array.</p>
  <p>For example the existing array is</p>
  <pre><code>[[1,2,3], [4,5,6]]
  </code></pre>
  <p>And now I have a new array which is</p>
  <pre><code>[7,8,9]
  </code></pre>
  <p>How can I get</p>
  <pre><code>[[1,2,3],[4,5,6],[7,8,9]]
  </code></pre>
  <p>I tried to use the spread operator, but haven't figured it out.</p>
  <p>Thanks</p>