title: Append element to an existing list in Node.js
body: <p>I know this question will seem to be a very common problem, but trust me I've spent hours searching on Google before asking this question...</p>
  <p>I have some data looking like this :</p>
  <pre><code>- book1
  ----- book1 number of pages
  ----- book1 number of chapters
  ----- book1 author
  - book2
  ----- book2 number of pages
  ----- book2 number of chapters
  ----- book2 author
  </code></pre>
  <p><strong>First question : how should I do ?</strong></p>
  <p>I've thought about :</p>
  <pre><code>let books_collection = {
   &quot;book 1&quot;:
      {
        &quot;number_of_page&quot;: 100,
        &quot;number_of_chapters&quot;: 5,
        &quot;author&quot;: &quot;Author 1&quot;
      },
  
   &quot;book 2&quot;:
      {
        &quot;number_of_page&quot;: 200,
        &quot;number_of_chapters&quot;: 7,
        &quot;author&quot;: &quot;Author 2&quot;
      }
  }
  
  </code></pre>
  <p>Does it looks good to you ? I will need to search easily into those data and save it to a Json file</p>
  <p> </p>
  <p><strong>Second question : how can I add a new book to this list?</strong></p>
  <p>When I search on Google, I find a lot of tutorials on how to add element to an ARRAY, but not to a list like that...</p>
  <p>How to add a new &quot;book 3&quot; to this list ?</p>
  <p> </p>
  <p><strong>Third question : how can I add a new subcategory to a book in this list?</strong></p>
  <p>If I want to create a new subcategory, like &quot;original_title&quot; , to an existing book, how to do that ?</p>
  <p>Thanks a LOT guys :)</p>