title: Backup worksheets in js, delete all and finally restore it
body: <p>Currently I'm triying to find a solution that helps me to storage the content of the worksheets in some place like localstorage for example.</p>
  <pre><code>async backupSheets() {
   await Excel.run(async (context) =&gt; {
    var worksheets = context.workbook.worksheets;
    worksheets.load('items');
    await context.sync();
    let wsBackup = worksheets;
    
    
    for (var i = 0; i &lt; worksheets.items.length; i++) {
      console.log(worksheets.items[i].toJSON());
      worksheets.items[i].delete();
    }
    //There will be some code to restore the workshets currently with:
    worksheets = wsBackup;
    //But it doesn't works.
  
    await context.sync();
   });
  }
  </code></pre>
  <p>The expected behavior is when I do the assigment <code>worksheets = wsBackup</code> it restore the worksheets that I saved before the delete loop.
  Currently this isn't working and I'm triying to find a workaround for this.</p>
  <p>An Excel scenario should be..</p>
  <ul>
  <li>Copy all the worksheets in a variable called <code>wsBackup</code></li>
  <li>Delete all worksheets except the last</li>
  <li>The proxy object that I used for it should be restored with the assigment of the backup <code>wsBackup</code></li>
  <li>The worksheets should be restored properly in the workbook</li>
  </ul>
  <p>The actual behavior that I got is all the steps except the restored worksheets.</p>