title: Prompt message box through custom menu on Google Sheets/App Script
body: <p>I have created a custom menu on Google Sheets with two options:</p>
  
  <pre><code>function onOpen(e) {
   var menu = SpreadsheetApp.getUi().createMenu('Custom')
   menu.addItem('Add new store', 'openForm')
   menu.addItem('Update Database', 'replacebackenddatabase') }
  </code></pre>
  
  <p>When a user selects "Update Database" I would like a message box to appear and ask for confirmation with "Do you want to proceed" and Yes/No basis. IF the user selects "Yes", I would like the function 'replacebackenddatabase' to run. If not, I would just like the message box to close and nothing to happen.</p>
  
  <p>How can I do this?
  Thank you!</p>